Steve Backshall: One year of expeditions, 10 world-first adventures, hundreds of near misses... Woman: Paddle, paddle, paddle!

Yoo-ooh!

Backshall: and many more moments we never expected... My, God, it's hissing.

It's hissing.

Backshall: close encounters with creatures that were awe-inspiring... Whoo hoo hoo!

Backshall: and fear-inducing...

It looks like he's coming back.

Backshall: plus close encounters with danger.

Big rock coming down.

Big rock coming down.

Woman: Aah!

Backshall: These are the stories of extreme adventures...

I hadn't mentally prepared myself for this bit to be dangerous.

Ugh... Backshall: chasing epic world-firsts.

It is truly one of the forgotten wonders of the world.

Backshall: I'm Steve Backshall, and this is "Expedition Unpacked."

Announcer: "Expedition Unpacked" was made possible in part by contributions to your PBS station from viewers like you.

Thank you.

Backshall: My year of adventures began in the flooded caves of Mexico...

It's really tight.

Backshall: continued with close encounters in the South American jungle... Ohh!

That is an absolute beauty!

Backshall: and close calls on the sheer cliffs of Oman.

Uh!

Big rock coming down!

Big rock coming down!

Backshall: But the closest call of all came in the Arctic... Go away!

Ha hah!

Backshall: with the world's largest land predator.

It's not having any effect.

He still keeps coming back.

♪ Backshall: The events that led to this alarming encounter began 5 days earlier.

I was in Greenland with a team of polar explorers to attempt a world-first-- to kayak the length of an icy fjord, a journey, sadly, now made possible by our warming world, but kayaking during ice breakup was perilous.

No one had ever attempted this before, so there was no way of predicting what was going to happen.

Before we could get paddling, we headed up to the ice cap to check on the condition of the fjord.

We were in the Arctic, traveling the Inuit way.

We've popped up above the clouds.

It's ridiculously beautiful.

♪ Honestly, you don't see a sight like that every day.

Ohh...hoo.

Backshall: It was June, and at that time of year, we should have been gliding over ice, not struggling through soft snow.

Is it different this year?

Yeah?

And now not so much.

Thin, very thin.

Backshall: When we reached the edge of the fjord, it was the same story out there, too.

Backshall: Joining me on this expedition was polar expert Sarah McNair-Landry.

Yeah.

5 years ago, we probably could have dogsledded this route at the same time of year.

Backshall: Yes.

It's pretty sure that what we're attempting just wouldn't have been possible 5 years ago.

Things are changing so quickly here.

Backshall: We knew the Arctic was warming, but our expedition was a chance to see firsthand how this early ice breakup was affecting the wildlife and the environment in this remote wilderness.

♪ Ahead of us lay 4 hard days and 30 long miles of paddling.

♪ Best practice is for us to be quite close together, certainly within visual distance of each other at all times, and if I'm getting too far ahead, then you guys need to shout me.

♪ Oh, oops.

Backshall: Navigating a route through unpredictable ice was borderline lethal.

♪ Kayaking is all about balance.

It was vital to keep our weight central and stay out of the freezing water.

[Crack] The air temperature was around zero, and overnight, the sea had iced up.

♪ The second anyone capsizes, goes over, comes out of their boat, it's gonna become a survival situation instantaneously.

To make matters worse, the ice was constantly moving and fast.

♪ I don't think there's anywhere else on Earth where you feel quite so small, quite so vulnerable, and quite so much like the environment is the master of you.

♪ Backshall: Our expedition medic Aldo Kane was watching our backs whilst keeping an eye on the pack ice.

It's already started to close in behind us.

We need to get out of here as quick as we can.

♪ Backshall: I pushed ahead to find a route through, but the ice began closing in all around me.

Oh, I don't like the look of this at all.

Can you see Steve there?

Can you see Steve?

♪ I can see his paddle.

♪ Backshall: I was cut off from the rest of the team.

There's just no way on.

Every single time I paddle, it turns into a blind alley, and you're stuck, and now I also have no way how we're gonna get back.

♪ Kane: Steve is on the other side of this ice here.

The general floe is all going that way.

That's 180 degrees from where we want to go.

We're going a long way the wrong way.

This isn't cool, is it?

Backshall: This was a humbling encounter... with the immense force of the Arctic.

We were powerless in its grip.

♪ The currents and wind were dragging the ice out to sea and us with it.

We needed to regroup and find a way out together.

Kane: Do you guys want to try pushing through on your boat?

Backshall: The filming boats had managed to stay with our kayaks.

Inuit boat captain Johann knew the mechanics of the ice well and tried to force a way through.

[Engine roaring] [Crack] The power of Johann's engine cracked open a channel... ♪ and we were finally reunited.

OK. You might want to have to power through these before they close.

♪ Oh, I think I see open water.

Backshall: It was a relief to escape the sea ice, but no cause for celebration.

This should be an unbroken, infinite stretch of white.

You should be able to drive a tank across it, but there's open sea, enough for us to paddle.

Earlier this year, the Arctic ice was measured, and it was the second lowest it had ever been on record.

Last year was the lowest, so the speed that things are changing here, the undeniable effect that it's having on the landscape and the rhythms of the Arctic are tangible.

There's something that's absolutely real.

Backshall: The warming Arctic wasn't just affecting the sea ice.

It was affecting the animals.

I'd expected the ice to be full of breeding seals, but up till now, we'd failed to see a single one.

Backshall: What is that little, black dot there?

McNair-Landry: That's a seal?

Backshall: Seals usually rest on the floating ice to make a quick escape if polar bears come prowling, but with the ice melting, the pup had been forced onto the frozen land.

Backshall: Oh, that's all right, little fella.

At this size, it's very difficult to tell what species it us, but by far, the most numerous up here is the ringed seal, and they're also the favorite food of the polar bear.

This one here could well-- it's young enough that it could well still be being seen by its mother.

♪ Oh, that is beyond cute.

♪ Backshall: The shoreline was the worst place for a young seal.

A polar bear would pick up on its scent from miles away, and any encounter with the Arctic's top predator would not end well.

♪ On overnight camps, we, too, needed to keep our wits about us.

Hah!

Oh, hah hah hah!

Oh!

Hey!

Hey!

♪ Backshall: It's wandering towards us.

♪ ♪ You can see already that it's smelt us because it's downwind of us.

It's lifting its head up, sniffing the air.

It's very, very aware that we're here.

♪ Backshall: At any other time, I would have been excited to see a bear, but this scenario was really worrying.

♪ Most of the time, bears will give you a wide berth, and that's what we hoped was going to happen... ♪ But as it was getting closer to us, its behavior changed.

It started yawning, shaking its head and shoulders, and all of those are signs of uncertainty.

Backshall: That yawn there is directed at us.

That's a threat display.

OK.

He's getting quite close now.

♪ Backshall: We'd planned for an encounter like this.

Coming together and making loud noises is the protocol to scare any bear away.

[Shouting and pounding] ♪ From there, he could cover this distance in a matter of seconds.

♪ [Click click] Hear the guys cocking their weapons.

Hey!

Hey!

Huh!

Hah!

Backshall: We were in this polar bear's habitat, and the very last thing we wanted to do was hurt him, but we had to scare him off.

Go on!

McNair-Landry: Want to put the flare off?

Yeah.

Hah!

Hah!

[Gunshot] Good job.

Backshall: Aiming to miss, we hoped the bright lights from our bear flares would drive him away... ♪ [Men shouting] Backshall: Hey!

Hey!

Hey!

♪ Backshall: But this bear wasn't stopping.

We got another flare, though.

Backshall: An encounter that should have been magical was turning into something really serious.

[Shouting and pounding] ♪ [Shouting stops] [Pounding continues] [Pounding stops] Yeah.

I think, hopefully, that will be enough to make him get on his way, but you could see he just was not frightened at all.

♪ Oh, it looks like he's coming back.

♪ So, so far, all the things that we've used are nonlethal.

We're using flares, firing into the air, but it's not having any effect.

He still keeps coming back.

♪ If he does decide to come for us, there's absolutely nothing else you can do but shoot it, and, seriously, that is the last thing that any of us want.

You can see he's just keeping on coming.

Backshall: We're all in the wildlife business and care deeply about animals.

We wanted to do everything we could to get rid of it and avoid hurt to the animal.

Hey!

Hey!

Hah!

Go on!

Go on!

Hah!

Hah!

Get out of here!

Go on!

Go on!

Go on!

Go on!

Hah hah!

McNair-Landry: Please, please, go on.

[Pounding] ♪ [Grunts] It's gone in the water?

[Splash] McNair-Landry: Yeah.

Backshall: The bear and our team were left unharmed from this encounter.

Backshall: So that's exactly what we were hoping for.

He's gone into the water.

He's swimming around us.

He finally decided that it wasn't worth the confrontation, but it is just pure and simple down to the fact that right now, food is so, so scarce, and he just has no option but to come and try out everything that could be food, and, it turned out, that was us.

Backshall: It was the ultimate close shave, brought on by the bear's changing world.

Backshall: Climate change up here is not something that you see on a graph or in stats and facts and figures.

It's in changes to every single day, and, you know, the fact that since the last ice age here at this time of year, this has just been a flat expanse of ice, and now it's not.

Does it need to be any more definitive than that?

What do we have to do before humanity wakes up?

♪ Backshall: The early ice breakup is having a huge impact on Arctic wildlife, but there are parts of our planet where animals still live as they always have done.

Our expedition to the jungles of South America took us to an unexplored and unmapped river in Suriname.

♪ We were on a mission to discover what animals lived deep in the rainforest, but we often got more than we bargained for.

Oh, it's a big rock right in the middle of the river.

Yeah.

♪ Yeah.

[Indistinct] Backshall: The only way to reach the heart of this impenetrable jungle was by helicopter.

[Helicopter whirring] The jungles of Suriname are arguably the most intact on the planet.

As much as 90% of this country is still covered in forest, and being down below all these trees, you could just see, thrashing through that would be horrific.

You would get absolutely nowhere.

Wow.

This is phenomenal.

We're literally about 5 feet off the water here.

Whoa!

Here we go.

Whoo hoo hoo!

Whoo!

It's like a roller coaster.

♪ Backshall: Instinct told me this jungle would be packed with animals.

Our challenge was finding somewhere to land.

Ah.

I see it!

I see it!

looks perfect.

I'm very glad that Gianni's such a good pilot because this is gonna be one heck of a landing.

Backshall: We were being dropped off in the heart of the largest expanse of pristine rainforest on Earth.

Kane: Good.

Backshall: Again by my side was friend and former Royal Marine Aldo Kane.

That is a pretty terrifying flight, isn't it?

Incredible.

There is just nothing in the world that compares to this moment.

It's you and the forest, and everything's about to begin.

It's impossible to replicate any other place than this, and we are the first human beings ever...

Ever, ever.

Ever to be here.

[Birds chirping] Backshall: From here, our plan was to paddle this unmapped river, a journey we'd guessed could take around a week.

To have any chance of seeing wildlife, we had to move through the forest quietly.

[Monkey chitters] Spider monkeys.

They're really curious.

Backshall: It was wonderful to see monkeys, but we were soon treated to a much rarer sight-- the harpy eagle.

♪ Backshall: You never see them this clearly.

This is arguably the biggest, heaviest, most powerful eagle in the world.

Wow.

This is unbelievable.

I cannot believe how much wildlife we've seen already.

We've only been on this river for a couple of hours.

Backshall: And the wildlife wasn't just in the canopy.

The jungle floor was also teeming with creatures.

Uh!

Ohh!

Whoa.

That is an absolute beauty!

This is a tiger rat snake.

It's not dangerously venomous, although they do have back fangs, and their venom is efficient on their prey, but he'll settle down in just a second.

Wow.

What a wonderful find.

They do feed on small mammals, sometimes on small birds, as well, and they're an active hunter.

They're a snake that goes out after their prey, climbing, physically examining every single hole and burrow that they can get close to in search of food, which is quite different to a lot of snakes you find in this part of the world that will just sit and wait and then will ambush predators.

♪ Backshall: As we pressed on into the heart of the jungle, our focus switched from the animals to the river itself.

♪ Oh, it's a big rock right in the middle of the river.

Yeah.

♪ Yeah.

[Indistinct] ♪ Ooh, that was a hell of a ride.

♪ Backshall: Each night, we made camp by the side of the river, another opportunity to explore.

I was just having a wash in the shallows, and all of a sudden, these massive fish came to within just this far away from me.

I'm gonna try and get some shots of them.

♪ [Panting] Backshall: The rivers of Suriname are home to numerous different kinds of fish, and these have a lethal reputation.

♪ Oh, my-- it's absolutely alive with piranhas-- I've never seen anything like it-- and the biggest black piranhas I've ever seen.

They literally are about the size of this net!

[Exhales] Wow!

I think the next stage has to be to catch one.

Backshall: Seeing these piranhas in such numbers was a good sign, a sign that that the river and the surrounding forests were untouched.

So this is the mighty black piranha, the largest species of piranha found in the world.

They're also known as the redeye piranha.

I think you can see why.

The reason that they haven't targeted me is that they focus on animals that are distressed and in trouble and wounded.

If I was injured, if I was bleeding, then I wouldn't last minutes in this water.

OK. Should we set him free?

Off you go.

Backshall: A jungle by day is only half the story.

Nighttime is when the predators come out to play.

Backshall: Tawny frogmouth, a most remarkable bird.

I cannot believe it let us get that close.

Oh, my goodness, that is amazing.

Oh, wow!

Unbelievable.

Kane: Oh, he's showing.

Backshall: Oh, yeah.

Croc.

♪ Kane: Yeah.

Got it.

As we're getting farther down the river, we're getting different kinds of crocodilian.

So this is a spectacled caiman.

When they're fully grown, he'll get to be 3 meters in length.

He'll be a really decent size.

To have lots and lots of apex predators means you've got to have lots and lots of food.

So if you've got a lot of crocs around, then it means the rivers are full of fish, and that's a really good sign for how healthy this river is, as if there was any doubt.

OK, fella.

Off you go.

♪ Backshall: I've been fascinated by spiders since I was a boy, but this jungle is home to one species that even I was keen to steer well clear of.

This would have to be every arachnophobic's worst nightmare.

It's a wandering spider, so named because they're very active hunters.

They go out, and they seek their prey, when they're prowling, and it's one of the ways that they can come into contact with human beings, and this has a call to being potentially the most venomous spider in the world, and being bitten by them is not good.

There is one added extra element to the wandering spider tale, which is that in its venom, it's got a unique component which affects men.

It's what's called a vasodilator.

It means that it makes your veins and your arteries expand, and in men, it can lead to endless painful erections and then total loss of any sexual ability afterwards.

Oh, they move so fast.

That's pretty nasty.

Let's get away from it before it does actually bite someone.

♪ Backshall: I'd dreamt of exploring this forest for nearly 20 years, but the reality was beyond imagination.

The deeper we went, the less fearful the animals seemed to become.

Backshall: Giant river otters.

There's a pair of them just downstream of us, and they're clearly intrigued by us, really interested.

♪ Kane: The wildlife that we are seeing has absolutely no fear of humans, no fear of this team.

I guess it's because they've just never had any human contact before, and that is a bit of a privilege, to be able to see that firsthand.

♪ Backshall: Wow!

♪ Capybara, the world's largest rodent.

They're about the size of an Alsatian dog.

They're huge, and-- oh, unbelievable.

Unusually for rodents, the eyes and the nostrils are right on top of the head, exactly as you'd expect in a crocodile... ♪ And phenomenal swimmers, able to duck below the surface for several minutes at a time.

And once they're under, they're gone.

Backshall: These animals are hunted by everything from jaguar to anaconda, and the water is their safe place.

Where was it?

Backshall: Nearby on the bank, we spotted something bigger and bolder.

♪ Our local guides Diego and Jan used an old Amerindian trick to bring this gentle giant out into the open.

[Whistles] Backshall: No way.

No way.

That is absolutely amazing.

Tapir right here, right here.

♪ [Whistles] This animal has never seen human beings before, doesn't know what we are, doesn't know to be afraid of us, and that is a very, very special thing.

[Whistles] This is the largest wild animal in South America, and to see one up this close is so, so rare.

This is one of the first animals that gets hunted out as soon as human beings move into an area.

♪ Well, that was an exercise in fieldcraft, and Diego and Jan just started whistling to it, and it whistled back, and over a few minutes, they kind of built up this little rapport, and then it just wandered out into the river right in between my cameraman and sound man's boats, just didn't seem to mind at all, completely oblivious, just not something you see anywhere else but somewhere like here where the animals haven't seen people before.

[Whistles] ♪ Backshall: In this day and age, wildlife encounters like these are rare.

These animals had never even seen people, let alone been hunted by them.

It was like traveling to the land that time forgot.

In most places on the planet, animals have been forced into being wary and remaining well-hidden.

Looking for elusive big cats in the scorched deserts of Oman, we had our fair share of close calls and near misses.

[Exhales] This is genuinely frightening stuff.

Uh!

Rock!

Ohh... Backshall: We were climbing a near-vertical rock face to find out whether it could be one of the last refuges of the Arabian leopard.

♪ There are only about 200 of them left in the world.

To track down these rare predators, I'd teamed up with wildlife expert Khalid al Hikmani.

So you've been working here for 12 years.

How many times have you actually seen the leopards?

Just only 3 times.

3 times?

Yeah.

So our chances, being here for a couple of weeks, are pretty slim.

Yep.

If you're lucky, maybe you will see some.

Oh, that would be amazing.

Backshall: Khalid had spent years studying the wildlife of the Dhofar mountains.

He captured images of foxes, hyenas... ♪ wolves... ♪ and honey badgers.

♪ What he didn't know was whether the leopards here were using ledges on the cliff face to hunt these prey animals.

To help him find out, we were going to climb the cliff face.

Look at that.

That is a dropping of a predator, but you can see little remnants of its prey inside of it-- lots of hair, vertebrae from smaller animals.

Pretty certain that that's leopard, Arabian leopard.

♪ Backshall: Arabian leopard had roamed southern Oman for millennia, but now with the human population expanding, their territory has shrunk.

Today they are almost extinct.

We hoped our cliff face might be one of their last hiding places, but climbing it was no easy task.

That is one imposing bit of rock... ♪ and it's so dramatic.

This escarpment, this cliff face, goes for about 50 kilometers in an unbroken line.

At its highest point, it's 1,500 meters high, and it just looks like a fortress.

♪ As imposing and dramatic as it is, the most remarkable thing about it is that no one has ever climbed there.

Backshall: Any climb is potentially dangerous, but I was especially nervous and for good reason.

A decade earlier, I'd fallen off a rock face, breaking both my ankle and my back.

Backshall: Getting onto something like this, which is super committing, is, yeah, proper frightening.

[Grunting] ♪ Number-one issue when you're nervous is hanging on too hard and using up too much energy when you don't need to, and that is exactly what I'm doing already.

I can feel myself doing it.

Ohh... ♪ Big rock coming down.

Everyone OK?

Kane, on radio: Yeah.

We're OK. Backshall: The rock was far more fragile than any of us had anticipated.

Even, like, one this size, even with a helmet on, it hits you in the shoulder or head, that'd certainly kill you.

♪ Uh!

Oh!

That's a biggie.

That's a biggie.

Don't go.

Don't go there.

Backshall: I carefully pulled myself inch by inch towards the relative safety of a narrow ledge.

Thank God for this particular pitch.

Yes.

Yeah, absolute beauty.

Come on!

Backshall: Having made it, I was desperate to find any signs of animals living up there... Wow!

Ooh, a big, spicy drop-off.

Backshall: But with the clouds rolling in, it was time to make camp for the night.

♪ ♪ Woman: Hey, Steve, come look at this.

This is a path?

Oh, my goodness, this is amazing!

This is like a highway for animals.

Yeah, look, look at this, like all trodden down.

These tracks here, the cloven hoof, those are from ibex, which is an utterly spectacular mountain goat incredibly at ease and at home on the very steepest of slopes, and we have a snake track.

That's quite crisp, as well.

That's-- I think that is almost certainly cobra.

These prints are from rock hyrax, and those are really specialized for living on pretty much vertical cliff faces, so you can very quickly see that our ledge system may be completely out of bounds for human beings, but it's certainly not to animals.

What's that there?

You don't expect to see a frog up here, and what it's doing here, I have absolutely no idea, but it does mean that somewhere round here is standing water.

Backshall: In fact, there was water all around us.

Backshall: That mist which is coming from the sea is one of the big reasons why there's so much life here.

Backshall: The moisture it provided was keeping the desert vegetation alive, which, in turn, was food for ibex and rock hyrax, and where prey animals go, predators follow.

I mean, this is an absolute thoroughfare.

That is a scrape.

Backshall: Scrapes are used to mark territories, especially by big cats.

Classically, scrape would be from leopard.

♪ I mean, it certainly seems like all the animals that leopard feed on are here.

♪ To be standing up here on this extraordinary ledge and seeing the signs of all the animals that have been here before us is absolutely incredible.

It's exactly what we came here for.

Backshall: Once the mist had lifted, we were able to set off on one last hard push to the top to meet back up with Khalid and tell him what we'd found.

Good work, Stephen.

Woman: Yeah.

Well done.

Ooh, shoot.

You all right, mate?

Yep.

OK. Oh, all this rock is horrible.

[Panting] Oh, sh-- big rock coming down!

Big rock coming down!

Woman: Aah!

This is so dangerous.

Just pulled off a chunk about the size of a television.

The end cannot come soon enough.

♪ Come on.

Come on, Backshall.

Let's have this.

Just last few moves.

Ohh, it's just there.

♪ Oh, and we've got a view of blue sky.

Uhh!

Yes!

Ha ha!

It's a long way.

Khalid!

Hi!

Thank you, my friend.

Hey, man, how are you?

Thank you so much.

How am I?

Yeah.

Honestly?

Yeah.

I'm pretty wrecked.

That's for you.

That is the sweetest cup of tea I've ever seen.

Mm.

Oh, that is nectar.

That is nectar.

Backshall: While we'd been climbing, khalid had been busy, too, collecting in remote cameras he'd left out around the mountain.

I couldn't wait to see what they'd captured.

Whoa!

♪ Backshall: There were agile ibex that we'd seen signs of on the ledge... ♪ and rock hyrax, too, both ideal prey for leopard.

Oh!

Oh!

Oh, my goodness!

Oh, it's absolutely beautiful.

Yes!

Come on!

Oh, that's the most amazing shot!

♪ Backshall: But it wasn't just one leopard.

It's two leopards.

Wow.

Al Hikmani: This one's female.

Man: Could be a male.

Coming after a female.

Yeah.

Backshall: This looked like a breeding pair.

[Scraping] Wow.

It's making a scrape right in front of the camera.

Yep.

Backshall: These were signs the male was ready to mate.

The climb and its close shaves had been worth it.

♪ We'd given Khalid strong evidence that the leopards were using the ledge to hunt, and to top it off, we'd been rewarded with footage of the animals themselves.

[Insects chirping] ♪ The images that we've seen of Arabian leopards wandering down these trails critically endangered, you know, there's only a handful of them left, and knowing that they're surviving and thriving here in this environment is incredibly exciting... ♪ but human beings are encroaching.

They're coming in from every side.

These last few truly wild places are everything.

The leopards on these cliffs are safe from humans.

Our climb had more than proved that.

For me and my team, accessing the seemingly inaccessible always provided us with hope for the future of the natural world.

♪ Deep underneath Mexico's Yucatan Peninsula, we were on a mission to discover new flooded cave systems.

Finding and mapping them would help protect them... ♪ but diving passageways barely big enough to squeeze through led to a life-or-death close call I'll never forget.

I was 800-feet underground when my dive gear got caught.

♪ I was trapped.

[Shouting] Backshall: Our cave exploration started with an arduous trek through jungle.

♪ But it's gonna take us all day long.

This is hard and heavy going.

♪ Backshall: Carrying heavy gear was business as usual for my expedition stalwart Aldo.

Every time we've been in the jungle, what do we have?

Jungle kit-- hammock, food, water.

Now we need jungle kit, climbing kit, descending kit, diving kit... Yeah.

free-diving kit.

Yeah, which explains why your load is so ridiculous.

[Birds squawking] You hear that sound, Aldo?

Kane: Say again?

You hear that sound?

That's motmot.

We must be close.

It's a great sound.

That is the voice of the cenote.

[Motmot squawking] These are motmots.

Backshall: When you're searching for an underwater cave, known locally as a cenote, the motmot bird is your friend.

These birds are never found far away from cenotes.

They live in and around them.

They nest in them, and that call, you hear that, and you know there's a cenote nearby.

They're kind of the closest thing this part of the world has to a bird of paradise.

The colors are preposterous, and the tails, they're just nuts, and they twitch it from side to side just like a pendulum, like that one there's doing right now.

♪ That is incredible, you know?

These birds are one of the wonders of the world.

You'd cross a continent to see something as beautiful.

Backshall: That motmot encounter was just what we needed.

They'd sign-posted the entrance to the cave we were looking for.

♪ Here goes nothing.

Kane: First man down.

♪ ♪ OK. ♪ [Panting] ♪ [Echoing] Backshall: Oh, this is so creepy!

Yeah.

Rather you than me.

♪ Huh.

[Exhales] Oh...

I'm in.

Ah.

Ooh, wow.

This is seriously creepy.

Oh... oh...ooh... Well, this is what it's all been about.

♪ ♪ Backshall: I soon realized I wasn't alone.

The cenote was home to shrimp, water scorpions, and even cavefish.

♪ Everything in that cave had evolved for life in a lightless world.

♪ The ghostly cavefish were blind and didn't react to my flashlight.

♪ These predators sensed everything by vibration, including their prey.

♪ They're extremely rare, but in that cave, I saw hundreds.

♪ OK. Should we head out?

♪ [Birds chirping] Backshall: Other caves we explored couldn't have been more different.

In those, we found predators that were much bigger.

♪ Backshall: There's a crocodile just sitting above us at the surface!

I'm gonna approach quite cautiously because I don't want to spook him.

There's two different species of croc found in this part of the world-- the American croc and the much, much rarer morelet crocodile, that probably more likely to be an American croc.

Now, that can get to be absolutely huge.

The biggest males could get to be 5 meters in length, and to see it like this early in the morning basking in the sun is absolutely magnificent.

[Regulator wheezing] Oh!

Amazing.

Great stuff.

Backshall: That close encounter with a croc was a real bonus, but not our main mission.

We were in search of unknown and unmapped passages.

By diving and mapping them, we could help to protect them, but it wasn't going to be easy.

We were preparing ourselves for some tight squeezes.

As far as my job is concerned of being in charge of safety, generally speaking on this expedition, there is nothing, absolutely nothing, I can do.

As soon as they leave the surface, they pretty much are on their own.

This is no rescue in there, and the worst-case scenario is, it's body recovery.

There is no half-measures, really.

Yeah.

It's pretty, pretty scary.

Backshall: I was going to be relying heavily on our dive leader Robbie Schmittner.

He's the best in the business, having already mapped nearly 600 miles of unexplored cave passageways in the area.

Schmittner: Sometimes I could get scared in the cave, too.

That's important.

If you lose that, you would be in a really, really dangerous spot.

We don't know if it's a very easy dive, what we're going to do.

We don't know what we find.

It's exploration, right?

Backshall: That's the nature of adventure, isn't it?

There has to be an element of the unknown, and there has to be hard work and failure for the thrill of success to be all the sweeter.

Cheers...to that.

Cheers.

To the day.

Cheers.

Cheers to that.

Cheers to that safe dive, safe journey, and safe return.

♪ Backshall: Next morning, I was nervous but laser-focused.

So I'm just running through all my checks, making sure that I've got backup lights in case my first, my second, my third fail, making sure that I've got enough air, working out what point in the air I have to turn back, and just running through all of these little, important checks in your mind that are just critical because once you get underwater, you can only think about very simple things.

It's not a time for complex problem-solving.

You need to have everything fixed in your head.

Just a little tiny thing goes wrong, and all of a sudden, your brain scrambles-- well, mine does, anyway-- and, yeah, so it's important to keep everything very, very simple.

♪ Backshall: I could mentally rehearse the technical practicalities beforehand, but what was harder to deal with was my own rising sense of fear.

An ever-increasing feeling of claustrophobia was engulfing me the deeper I went and the further I got from safety.

♪ We found ourselves inside stunning caverns decorated with thousands of stalactites and stalagmites... ♪ but bulky dive tanks and these spikes were a potentially lethal combination.

♪ I couldn't see it, but my cylinder straps had caught on the tip of a stalactite.

♪ I tried to free myself by rolling sideways, but that only made things worse.

I was going nowhere.

♪ At most, I had half an hour of air in my cylinder.

Panicking, I was using it up too quickly.

♪ Robbie was just ahead of me, and I could see he was willing me to calm down and take it easy.

♪ Robbie's reassurance was what I needed.

I managed to free my tank and finally emerged into the most extraordinary chamber.

♪ The mirror image was an optical illusion caused by a shallow pocket of air trapped against the roof of the cave.

♪ And then, a world-first discovery.

♪ It had taken guts to get here, but it was worth every close shave.

♪ Our flashlights were illuminating a part of the world that no human had ever seen before.

Together with Robbie, we'd found new, pristine caves to add to our understanding of this unique ecosystem.

♪ In Yucatan, as in everywhere we journeyed to, our pursuit of world-firsts had pushed us to the very edge of our mental and physical limits.

♪ Come on!

♪ The thing that sets us apart as a species, as human beings, is our desire to explore, to discover, to solve puzzles.

When I was a kid, I was so disappointed at thinking that I'd been born in the wrong generation and that all of the exploration had been done, and I was wrong.

There are still fabulous, dark parts of the world that are left to be explored.

♪ "Expedition Unpacked" is available on Amazon Prime video.

♪ ♪