0:00:04 > 0:00:05The Heart of Borneo.
0:00:05 > 0:00:11A rugged and treacherous landscape of forests, ravines and mountains.
0:00:12 > 0:00:15It hides an extraordinary variety of wildlife,
0:00:15 > 0:00:19but these forests are disappearing fast.
0:00:20 > 0:00:24For the past five weeks, a team of scientists, mountaineers
0:00:24 > 0:00:28and filmmakers have been exploring this amazing wilderness.
0:00:29 > 0:00:32The expedition has now split into two groups.
0:00:32 > 0:00:37To the west, Steve and Justine are attempting a daring descent into the middle of a mountain.
0:00:37 > 0:00:40Oh, my God.
0:00:42 > 0:00:50To the south, Tara, Tyrone and George are heading deeper into the pristine and unexplored jungle.
0:00:52 > 0:00:57These journeys into the wilderness are the climax of the whole expedition.
0:01:12 > 0:01:16In these limestone mountains, what seems like solid ground
0:01:16 > 0:01:21can suddenly collapse into a deep underground abyss.
0:01:26 > 0:01:29Steve Backshall and Justine Evans have been clinging onto ropes
0:01:29 > 0:01:32while a tropical storm has blown over them.
0:01:34 > 0:01:37Now, with the danger past, they can continue their journey
0:01:37 > 0:01:40into the enormous chasm known as Solo.
0:01:41 > 0:01:45It's an isolated habitat that's lain untouched for millennia.
0:01:56 > 0:02:00Watch the ground when you get down, Justine, it's razor sharp.
0:02:00 > 0:02:06- All the trees are very, very spindly compared to what they are just on the other side of the hole.- Yeah.
0:02:06 > 0:02:12- Must have permanent rain, cos when it's not raining, you've still got drips all the time.- Yeah.
0:02:12 > 0:02:18They're experienced climbers, but Steve is also a biologist and Justine's a wildlife camerawoman.
0:02:18 > 0:02:22The third climber is Tim Fogg, in charge of safety.
0:02:24 > 0:02:28Their aim - to make a rapid assessment of the animals and plants
0:02:28 > 0:02:32that live at the bottom of this enormous collapsed cave.
0:02:33 > 0:02:39It seems that this cave roof would have collapsed on what was then a huge cavern,
0:02:39 > 0:02:45at least a million years ago and this eco-system has been, you know, growing like this ever since then.
0:02:48 > 0:02:54It's tough, it's really hard walking because this is just...
0:02:54 > 0:02:58this jaggedy, this is what we're walking on, walking on lumps of this
0:02:58 > 0:03:02and it's all shifting and you're falling over all the time.
0:03:02 > 0:03:03It's just dangerous.
0:03:03 > 0:03:09On all sides, there are gigantic stalactites formed over thousands of years.
0:03:11 > 0:03:16Every single one of these stalactites is so unique, you can almost play them like a cave xylophone.
0:03:18 > 0:03:20MUSICAL NOTES RING OUT
0:03:20 > 0:03:21MUSICAL NOTE RINGS OUT
0:03:21 > 0:03:23HOLLOW TAPPING
0:03:23 > 0:03:25Ha! That one's not so good.
0:03:25 > 0:03:27Cut off from the outside world,
0:03:27 > 0:03:31this habitat is completely unknown to science.
0:03:32 > 0:03:35Both Justine and I are generalists.
0:03:35 > 0:03:40What I'd really like to do would be to bring Tyrone and George and Tara down here
0:03:40 > 0:03:45who are all specialists in their fields and get them to suss it out.
0:03:45 > 0:03:51But at the moment, they're halfway up the Segah river and probably half drowning, so that's not an option.
0:03:57 > 0:04:02This one's a tricky rapids cos the water's coming at us from the side and from in front.
0:04:03 > 0:04:07Dr Tara Shine is leading a group up the remote Segah river.
0:04:07 > 0:04:13It's the first time a team of biologists have ever studied this area of rainforest.
0:04:15 > 0:04:19Heavy with gear, the narrow wooden boats are being pushed to the limit
0:04:19 > 0:04:22by expert boatmen from the village downstream.
0:04:22 > 0:04:26They're trying to get the team as far upriver as possible.
0:04:37 > 0:04:40This boat is the heaviest one - it's got all the food in it.
0:04:40 > 0:04:45It got stuck halfway up the rapids, everybody had to jump in and pull it out.
0:04:45 > 0:04:49If it gets any more exciting than this, I won't be able to cope!
0:04:51 > 0:04:55They're now moving rocks to make getting the boats up easier.
0:04:59 > 0:05:02Oh, look at the flying bats! Quick, quick, quick, look!
0:05:02 > 0:05:05Circling fruit bats.
0:05:06 > 0:05:08A little bit eerie, isn't it?
0:05:08 > 0:05:11Oh, my God, I've never seen so many of them.
0:05:13 > 0:05:19They want to make a first assessment of the diversity of Segah's undisturbed wildlife.
0:05:20 > 0:05:25Oh, I think it's really exciting. Definitely no other film crew has been up this river
0:05:25 > 0:05:29to capture the beauty of it and bring that back for people to see.
0:05:29 > 0:05:33In the team, insect expert Dr George McGavin
0:05:33 > 0:05:37and reptile and amphibian specialist Professor Tyrone Hayes.
0:05:37 > 0:05:43I'd like to see, hopefully, some snakes or pythons that live along the water.
0:05:43 > 0:05:46There's a number of aquatic turtles that one might find.
0:05:46 > 0:05:48Keeping my eyes open.
0:05:50 > 0:05:57The most amazing thing about being here is that this is the richest place on Earth in terms of species,
0:05:57 > 0:06:02so in there are far more species than anywhere else on Earth.
0:06:02 > 0:06:06It's pristine jungle, I mean it's the stuff of Jungle Book.
0:06:06 > 0:06:10I mean, really, it's clear, clear streams,
0:06:10 > 0:06:15beautiful, untouched forest, clear blue skies - I mean, perfection.
0:06:15 > 0:06:19And we've got to come right into the depths of it
0:06:19 > 0:06:21and very few people get to do that.
0:06:21 > 0:06:25This part of the jungle is totally unprotected.
0:06:25 > 0:06:30The team wants to find evidence that this pristine jungle should be preserved forever.
0:06:30 > 0:06:34If not, it could soon be felled for timber.
0:06:40 > 0:06:43Fortunately, Solo is protected within Mulu National Park.
0:06:43 > 0:06:47Yet absolutely nothing is known of what lies at the bottom.
0:06:50 > 0:06:52Virtually no soil at all
0:06:52 > 0:06:57and everything seems to be growing on jaggedy bits of rock.
0:06:58 > 0:07:04You see this single-leaf plant has its roots spread out amongst the rock.
0:07:04 > 0:07:07These are incredible plants, almost like little sundials.
0:07:07 > 0:07:13The leaf turns throughout the day to maximise the sunlight it receives,
0:07:13 > 0:07:17especially important here, where you've only got a beam of sunlight
0:07:17 > 0:07:18coming down almost at noon
0:07:18 > 0:07:23and the rest of the day, almost everything in here's gonna be in the shade.
0:07:23 > 0:07:27It's a gloomy, windless world with a constant fall of water from above,
0:07:27 > 0:07:30creating a unique microclimate.
0:07:33 > 0:07:38Just documenting as much as possible so we can work out what's growing down here.
0:07:38 > 0:07:40I didn't think there'd be many mammals,
0:07:40 > 0:07:44but we've seen lots of little footprints of rodents,
0:07:44 > 0:07:48we've seen signs of snakes, snake tracks -
0:07:48 > 0:07:50it is absolutely incredible.
0:07:52 > 0:07:55Just found this rather extraordinary-looking little bug,
0:07:55 > 0:07:58probably related to the assassin bugs
0:07:58 > 0:08:03which is why I'm holding him so carefully cos assassin bugs have a very painful bite.
0:08:03 > 0:08:07How I recognised this one is you can see just there, at the front of the head,
0:08:07 > 0:08:12is a curled beak which they use for piercing into their victims
0:08:12 > 0:08:16and sucking out their insides, which is pretty gruesome.
0:08:16 > 0:08:21But the amazing thing about this one is all that incredible algae
0:08:21 > 0:08:25that's growing all over its body, or even, I suppose, could be a part of its body
0:08:25 > 0:08:30and that gives it fantastic camouflage on the walls of this cave here.
0:08:30 > 0:08:33Crazy-looking little creature. Ooh!
0:08:40 > 0:08:43These are actually quite small boats
0:08:43 > 0:08:47and they rock, as you can see, quite a lot
0:08:47 > 0:08:49because they haven't got much draught.
0:08:49 > 0:08:55If you move even slightly, the whole thing starts to rock, so it's quite an experience.
0:08:55 > 0:09:01The further the team push up the Segah, the shallower and rockier the river becomes.
0:09:01 > 0:09:04Just how far they get is up to the experienced boatmen.
0:09:08 > 0:09:14Quick, quick, quick, look. Monitor lizard, he was just sitting, basking in the sun on the bank.
0:09:14 > 0:09:18The team need to be quick if they're to see any creatures close up.
0:09:19 > 0:09:23I thought it was a crab or a water scorpion. so I thought, "I'll get the net."
0:09:23 > 0:09:25EXCITED SHOUTING
0:09:25 > 0:09:29What they've actually found is a freshwater turtle.
0:09:29 > 0:09:30It's a small female.
0:09:30 > 0:09:33Amazingly soft, it's just like rubber, isn't it?
0:09:33 > 0:09:37They sit on the bottom, stick their head up - see the nose is at the tip?
0:09:37 > 0:09:40Then when a fish comes, they shoot their head out and catch the fish.
0:09:40 > 0:09:43I've been bitten by one a little bigger than this in the US.
0:09:43 > 0:09:45But it's very painful.
0:09:45 > 0:09:47Look what's done to me net!
0:09:47 > 0:09:48Completely wrecked it.
0:09:52 > 0:09:54There's only one way out of Solo -
0:09:54 > 0:09:59an arduous 160-metre climb back up the ropes.
0:10:01 > 0:10:03But at the deepest part of this crater,
0:10:03 > 0:10:07Steve and Justine make an intriguing discovery.
0:10:07 > 0:10:10Oi-yah. How about that?
0:10:10 > 0:10:11It's amazing.
0:10:11 > 0:10:16There's a small opening that appears to lead further into the mountain.
0:10:16 > 0:10:19It could even be another way out.
0:10:19 > 0:10:23Everything down there is totally uncharted.
0:10:23 > 0:10:26No-one has any idea what's down there.
0:10:26 > 0:10:30We'd certainly be the first people to go down there.
0:10:30 > 0:10:34The idea that we could be exploring a completely new cave passage
0:10:34 > 0:10:37to come out at the bottom of the mountain is just bonkers.
0:10:37 > 0:10:40I can't believe we can go through there and get out the other end.
0:10:40 > 0:10:44It's a long shot, but these mountains are riddled with holes.
0:10:44 > 0:10:49The tiny opening could be the entrance to a whole network of undiscovered caves.
0:10:52 > 0:10:57On the river, Tara and Tyrone set up their hammocks.
0:10:57 > 0:10:58That's as much as you can have.
0:11:00 > 0:11:05While George goes for a closer look at the forest.
0:11:05 > 0:11:09Ah, wow! That is a caterpillar
0:11:09 > 0:11:11and it's absolutely gorgeous.
0:11:11 > 0:11:13It's head end, which is up here,
0:11:13 > 0:11:15has got these big eye spots on.
0:11:16 > 0:11:20If I turn it round, you'll see the head tucked underneath.
0:11:20 > 0:11:24I've seen things in the same group and it's always said that they look like snakes.
0:11:24 > 0:11:29I suppose if you were a bird and it was angled like that,
0:11:29 > 0:11:31you might think twice about it.
0:11:34 > 0:11:41In the jungle, insects that aren't camouflaged normally have a very good way of defending themselves.
0:11:41 > 0:11:45Up here is an ant nest and if I turn it over...
0:11:45 > 0:11:47Ooh, ooh, ooh - they're stinging!
0:11:47 > 0:11:53Ooh, ah! They're coming swarming out and they're attacking me. Ah! ha, ha, ha!
0:11:53 > 0:11:55You can see how active they are and fierce.
0:11:55 > 0:12:01There are literally thousands and thousands of ants there and they're all mean and mad as hell.
0:12:01 > 0:12:03Ooh!
0:12:03 > 0:12:07Oh, oh, oh, oh, oh! Ow, jeez!
0:12:07 > 0:12:09Oh!
0:12:10 > 0:12:12Ooh! They're everywhere!
0:12:12 > 0:12:17How can they get everywhere in such a short time? I was only holding it for ten seconds.
0:12:24 > 0:12:27In Solo, the team rest up for the night,
0:12:27 > 0:12:30but Steve can't resist getting a closer look
0:12:30 > 0:12:33at what lurks in the darkness.
0:12:33 > 0:12:38This really is the creature of most people's worst nightmares.
0:12:38 > 0:12:42This is a venomous centipede and it's brilliantly adapted,
0:12:42 > 0:12:47actually perfectly adapted, to living and hunting in the dark.
0:12:47 > 0:12:51Possibly the worst thing about it though is the way they move.
0:12:51 > 0:12:53If I give a little tap and you see it run,
0:12:53 > 0:12:57honestly, you will see it in your nightmares for weeks. It's horrid.
0:13:03 > 0:13:07I might be a bug lover, but that really gives me the creeps.
0:13:09 > 0:13:12Corned beef hash. We'll be having it though with rice,
0:13:12 > 0:13:16we must have rice three times a day, otherwise the sky will fall down
0:13:16 > 0:13:20and some eggs, so lots of protein.
0:13:20 > 0:13:22Today was tough.
0:13:22 > 0:13:29I fell and busted my knee, I got dragged several metres by the boat,
0:13:29 > 0:13:30my feet hurt, my feet are tired,
0:13:30 > 0:13:33a huge spider just jumped over my shoulder...
0:13:33 > 0:13:36- Cor, look at that! - That's the biggest one I've seen yet.
0:13:36 > 0:13:39That's a cracker. It's a male, it's a Sparassidae,
0:13:39 > 0:13:43Huntsman spider, Heteropoda absolutely gorgeous.
0:13:44 > 0:13:45Awesome.
0:13:45 > 0:13:48This place is a bug hunter's dream.
0:13:48 > 0:13:52I'm sure individuals in the past have been here before
0:13:52 > 0:13:58because it would be very hard to find anywhere, on Earth where humans haven't been
0:13:58 > 0:14:01except perhaps caves and ocean floors,
0:14:01 > 0:14:05but... this is the real deal.
0:14:05 > 0:14:08It's completely unspoilt.
0:14:10 > 0:14:14Tomorrow's cave descent will be fraught with danger.
0:14:15 > 0:14:21They have these things called false floors and they're literally suspended and you walk onto them
0:14:21 > 0:14:24and if you're lucky, they hold and if you're unlucky, you go though them
0:14:24 > 0:14:27and the whole lot can just go down like a crust.
0:14:27 > 0:14:31- Got to watch where we're putting our feet.- Do be very careful
0:14:31 > 0:14:36and if you get that hollow sound when you're walking, you want to be very aware.
0:14:48 > 0:14:52Last night I woke up in a cold sweat just imagining myself
0:14:52 > 0:14:57stuck in a hole with cave crickets and centipedes swarming all over me.
0:14:57 > 0:14:59Thoroughly unpleasant.
0:15:02 > 0:15:05Last time we'll see that for a while.
0:15:05 > 0:15:07The other hole, down below us,
0:15:07 > 0:15:09just uninviting darkness.
0:15:12 > 0:15:16It's pretty treacherous to walk down these rocks
0:15:17 > 0:15:19and it's, it's all loose.
0:15:20 > 0:15:22I'm quite nervous now.
0:15:22 > 0:15:23Oh, God.
0:15:35 > 0:15:42Wow! We're just entering through this, this high sided area
0:15:42 > 0:15:47with these ferns and palms and it's just like the Lost World in here.
0:15:47 > 0:15:50It's one of the most fantastically beautiful places I've ever seen.
0:15:50 > 0:15:55Dripping with mosses and ferns, just breathtaking.
0:15:56 > 0:16:02These are great, all the roots of the trees trying to get down to water level to absorb water.
0:16:04 > 0:16:07It's a totally different atmosphere to the rest of the river
0:16:07 > 0:16:10cos all of a sudden, it just closes in around you.
0:16:17 > 0:16:21Deep underground, the narrowing in the rock is rather more extreme.
0:16:24 > 0:16:27I can see the way on and it looks as if it's getting bigger,
0:16:27 > 0:16:32but just before it is a blade of rock which we've got to go over the top of.
0:16:32 > 0:16:35It looks as if I can just get my body through it.
0:16:35 > 0:16:37- So it's a squeeze.- It's a squeeze.
0:16:37 > 0:16:42If Tim's going to struggle to squeeze through, how the heck am I going to get through?
0:16:42 > 0:16:49We're pretty much the same height, but I reckon I weigh about half as much again as Tim. All those burgers.
0:16:56 > 0:16:59Ooh, that's very tight.
0:16:59 > 0:17:03If you get to a stage where it's getting difficult, go back out.
0:17:03 > 0:17:07- Squashing everything.- Oh!
0:17:07 > 0:17:09How d'you feel that was, Steve?
0:17:09 > 0:17:12I'm not built for caving.
0:17:12 > 0:17:14Oh, we'll get through now, Steve.
0:17:14 > 0:17:18Steve's wedged underground with thousands of tonnes of rock above him.
0:17:18 > 0:17:21Steady with your feet. You can crouch down now.
0:17:23 > 0:17:27Oh, God. This is the kind of thing I've been seeing in my nightmares.
0:17:27 > 0:17:30You've got to push one arm through.
0:17:30 > 0:17:31OK.
0:17:36 > 0:17:38Yeah. Good man.
0:17:51 > 0:17:53HE EXHALES SHARPLY
0:17:53 > 0:17:56If it gets any tighter than that, I'm stuffed.
0:18:00 > 0:18:04The Segah team have found the perfect place to make camp
0:18:04 > 0:18:06and to explore the jungle.
0:18:06 > 0:18:10I was sitting over there with the guys and we heard this barking sound
0:18:10 > 0:18:14and they jumped up and started shouting "monyet", which is monkey,
0:18:14 > 0:18:18so then we saw these long-tailed macaques way up in the trees over here.
0:18:18 > 0:18:23That's the first primates we've seen on this river.
0:18:23 > 0:18:25It was absolutely amazing.
0:18:25 > 0:18:30What's becoming clearer and clearer is that there's an awful lot here worth looking after
0:18:30 > 0:18:35and that, you know, it looks like it would be good idea
0:18:35 > 0:18:39for more steps to be taken to safeguard this area into the future.
0:18:44 > 0:18:45Whoop!
0:18:45 > 0:18:47Ooh, listen to that!
0:18:47 > 0:18:49Whoop!
0:18:49 > 0:18:51God, it's big in there.
0:18:51 > 0:18:57Hundreds of metres underground, they find that the pothole has opened out into a massive chamber.
0:19:00 > 0:19:02Tim, it's huge.
0:19:02 > 0:19:03I can see.
0:19:03 > 0:19:06I can see 45, 50 metres in front of me, at least,
0:19:06 > 0:19:09and above us, it looks even bigger, Steve.
0:19:09 > 0:19:11This is great. Look at that.
0:19:16 > 0:19:19It's absolutely vast.
0:19:19 > 0:19:24I'm 100% sure this is the first light that has ever been in here.
0:19:24 > 0:19:28We're the first people ever to set foot in here.
0:19:25 > 0:19:28First humans ever to see that view
0:19:28 > 0:19:31out through that chamber and these roofs.
0:19:32 > 0:19:34Awesome.
0:19:35 > 0:19:36That is quite something.
0:19:37 > 0:19:40This is true, original exploration.
0:19:41 > 0:19:48Finding a way through this labyrinth won't be easy, there are so many dead ends.
0:19:48 > 0:19:51They must remember each and every twist and turn -
0:19:51 > 0:19:53getting lost would be fatal.
0:19:54 > 0:19:58Just found an absolutely perfect skeleton.
0:19:58 > 0:20:03It almost looks like a fossil, which of course in due time, it will be.
0:20:03 > 0:20:08It's not a bat, as you can see that the rear limbs are pretty much the same size as the fore limbs.
0:20:08 > 0:20:11That's the lower jawbone there,
0:20:11 > 0:20:14that's the body twisting round there to the back limbs
0:20:14 > 0:20:17and this jawbone here's very interesting.
0:20:17 > 0:20:20I'm guessing some kind of rat.
0:20:20 > 0:20:23That's what we're going to look like in a few hundred years.
0:20:23 > 0:20:25Amazing stuff.
0:20:26 > 0:20:30Far from the death and sterility of the cave,
0:20:30 > 0:20:34George is surrounded by countless forms of life.
0:20:36 > 0:20:38Hee, hee, hee!
0:20:39 > 0:20:45I'm not at all upset that I was unable to go down a big hole,
0:20:45 > 0:20:48though I'm sure there are very interesting things there,
0:20:48 > 0:20:53but this is just...breathtaking.
0:20:58 > 0:21:00That's a huge cicada.
0:21:02 > 0:21:04The whole of the abdomen is hollow.
0:21:04 > 0:21:05INSECT CROAKS
0:21:05 > 0:21:07Hear that?
0:21:07 > 0:21:11That's probably one of the ones that wakes us up in the morning.
0:21:11 > 0:21:14Look at that, it's a beauty. It's an absolute beauty.
0:21:14 > 0:21:19The sheer variety here is, is just staggering.
0:21:19 > 0:21:20Ah, wow!
0:21:20 > 0:21:23That's the biggest bee in the world.
0:21:23 > 0:21:25Look at it. There it is.
0:21:25 > 0:21:30I haven't seen one before in the wild. In collections, in museums, yes.
0:21:30 > 0:21:35That Uranid moth is certainly the biggest moth I've seen flying,
0:21:35 > 0:21:37the biggest cicada I've seen flying
0:21:37 > 0:21:40and the biggest bee I've seen flying in the wild.
0:21:40 > 0:21:43There's a huge variety of stuff here.
0:21:43 > 0:21:45Look at these guys, look at these.
0:21:47 > 0:21:53Further along the riverbank, Tyrone and Tara are on the hunt for snakes.
0:21:53 > 0:21:57There are 150 species of snake in Borneo
0:21:57 > 0:22:01and many come out at night in search of prey.
0:22:04 > 0:22:08Tyrone catches a venomous mangrove snake.
0:22:09 > 0:22:10Amazing.
0:22:12 > 0:22:15But this isn't what he's really after.
0:22:16 > 0:22:21While gathering wood, one of the boatmen caught a glimpse of a far more dangerous snake.
0:22:23 > 0:22:25Young man saw a cobra earlier
0:22:25 > 0:22:29and says it's in a nest and though he was reluctant,
0:22:29 > 0:22:32we've convinced him to show us where it is.
0:22:32 > 0:22:37Cobras, of course, are venomous and can be very dangerous and deadly.
0:22:38 > 0:22:42I tell you, it'd be really freaky if I was here on my own.
0:22:42 > 0:22:46I wouldn't be here without someone who knows where they're going.
0:22:50 > 0:22:53Oh, jeez, there it is. It's moving, you guys.
0:22:53 > 0:22:56It's a female on a nest of leaves.
0:22:57 > 0:23:01- Oh, wow, look at that.- Looks like a cobra all right. A king cobra.
0:23:01 > 0:23:05It moves fast enough that this is as close as I'm going to get.
0:23:05 > 0:23:06Wow, awesome.
0:23:12 > 0:23:16The king cobra's raised hood is a clear threat display.
0:23:16 > 0:23:18It says, "back off or I'll bite."
0:23:19 > 0:23:22I like the motion, I like the mystery,
0:23:22 > 0:23:25I like the way that they move...
0:23:25 > 0:23:27This one's particularly beautiful,
0:23:27 > 0:23:30yet probably one of the more deadly snakes in the world.
0:23:30 > 0:23:34This female is protecting a clutch of up to 40 eggs.
0:23:34 > 0:23:37Seeing a king cobra is a good sign.
0:23:37 > 0:23:41They're top predators, eating only other snakes.
0:23:41 > 0:23:44They can only survive in a rich and diverse habitat.
0:23:45 > 0:23:50She's gone under the leaves, we don't know where she could pop up
0:23:50 > 0:23:52and she also may have a mate around,
0:23:52 > 0:23:54so I think we've outstayed our welcome.
0:23:54 > 0:23:56Let's back up.
0:23:56 > 0:23:57OK, bye, cobra.
0:23:59 > 0:24:01That was awesome.
0:24:05 > 0:24:08On the riverbank, George sees his bug sheet
0:24:08 > 0:24:11as an encouraging measure of the health of the jungle.
0:24:11 > 0:24:15Ecosystems are made up by small things
0:24:15 > 0:24:19and without insects, you simply wouldn't have large animals
0:24:19 > 0:24:21and all the rest, cos that's what they eat.
0:24:21 > 0:24:24If you removed all the insects,
0:24:24 > 0:24:28ecosystems would collapse basically, in a year, I reckon.
0:24:28 > 0:24:29Oh, wow.
0:24:31 > 0:24:33This is, this is more like it,
0:24:33 > 0:24:37I mean, this is, this is evidence
0:24:37 > 0:24:43that this area is incredibly rich, very, very pristine, if you like.
0:24:43 > 0:24:45Oh, look at that! Oh, wow!
0:24:53 > 0:24:59In the cave, every potential way through is blocked.
0:25:00 > 0:25:06- I'm afraid we're back to where we started and we've checked every lead.- Oh, no.
0:25:06 > 0:25:09We've been at it for a fair few hours now
0:25:09 > 0:25:15and there just doesn't seem to be any way out of this huge chamber.
0:25:15 > 0:25:18I really don't think we can push on any more.
0:25:18 > 0:25:22I think time-wise, we've just run out, lights are beginning to go...
0:25:23 > 0:25:26But this is a true labyrinth.
0:25:26 > 0:25:31- Just feast your eyes on something that nobody else has ever seen. - Yeah.
0:25:56 > 0:25:58On the Segah, the team has also come to a halt.
0:26:04 > 0:26:08The river is so shallow that the boats can go no further.
0:26:08 > 0:26:10It's time to turn back.
0:26:13 > 0:26:18- I'm a bit sad that that's all behind us now.- Well, you can't have everything, can you?
0:26:18 > 0:26:21You can hardly expect to stay here forever.
0:26:21 > 0:26:23Yeah, no.
0:26:23 > 0:26:25Back to reality.
0:26:25 > 0:26:27We're off.
0:26:29 > 0:26:32Oh, that's nice - look at that, daylight.
0:26:32 > 0:26:34Oh! I'm glad to see that.
0:26:38 > 0:26:41I've never been gladder to see blue sky.
0:26:44 > 0:26:48It's quite something to be somewhere no-one's ever been before,
0:26:48 > 0:26:51but as far as I'm concerned it can stay that way.
0:26:52 > 0:26:53THEY LAUGH
0:26:53 > 0:26:58They've reached daylight, but they still face a haul out of the chasm
0:26:58 > 0:27:00and an arduous jungle trek.
0:27:02 > 0:27:06We're now leaving the Lost World for the last time. This is it, we're going.
0:27:06 > 0:27:12It's been great being here in Borneo seeing new environments, new animals, new species.
0:27:12 > 0:27:14It's been so magical up here,
0:27:14 > 0:27:18little bit apprehensive about going back to reality.
0:27:18 > 0:27:21Beautiful. I hope it remains unspoilt forever.
0:27:21 > 0:27:25We've made a real decision to go to places deliberately,
0:27:25 > 0:27:27that people haven't been to before
0:27:27 > 0:27:32and it makes things a lot harder, but the sense of achievement is that much greater.
0:27:32 > 0:27:34It's been incredible. Great adventure.
0:27:34 > 0:27:39The expedition is now over. In the last six weeks,
0:27:39 > 0:27:42they've explored throughout the mountains of Borneo,
0:27:42 > 0:27:44from the highest jungle peak...
0:27:44 > 0:27:46Stunning.
0:27:46 > 0:27:49..to deep underground.
0:27:49 > 0:27:51Absolutely vast.
0:27:51 > 0:27:54They've filmed Borneo's spectacular animals.
0:27:55 > 0:27:58- They've been bitten.- Ooh-ya, ow!
0:27:58 > 0:28:01They've bled. And they've got thoroughly carried away.
0:28:04 > 0:28:10They've found over 200 species, from the rare to the deadly,
0:28:10 > 0:28:12the beautiful to the plain weird.
0:28:12 > 0:28:13Ah, wow!
0:28:13 > 0:28:19The discoveries of the expedition will now add to the growing body of scientific evidence
0:28:19 > 0:28:23proving that this threatened rainforest needs protecting forever.
0:28:23 > 0:28:28It's the living, beating heart of Borneo.
0:28:38 > 0:28:40There he is, there he is.
0:28:40 > 0:28:43That's what we share the toilets with here!
0:28:47 > 0:28:49Absolutely extraordinary.
0:28:51 > 0:28:55Subtitles by Red Bee Media Ltd
0:28:55 > 0:28:56Email subtitling@bbc.co.uk