Waking up to a rainy Rotorua, we rolled out of town and on through 3 hours of sheep-filled fields to the west coast to visit the Waitomo Caves.

Traditionally used as burial places for Maori chiefs, the limestone caves on the west coast had been mostly forgotten until recently when some avid cavers persuaded the land-owning farmers of their money-earning potential. Waitomo is the most famous of these accessible caves, its glow-worm covered cavities and fast flowing underground rivers making it the ideal location for some more kiwi adventure tourism. We chose the more tame Blackwater Tubing option, which we understood as gently floating down an underwater river seated on giant inner tubes, underneath a constellation of glow-worms. This was one element of the tour...

Our guide Brad was in his early twenties and sported a weird half-shaved / half-mullet haircut. As we got kitted up he regaled us with tales of his adventures with his caving-buddies, including one trip where they spent four days underground exploring a cave on the south island. Clearly a strange kid, he also seemed to suffer from a kiwi version of tourrettes, whereby he randomly punctuated his sentences with the word 'Sweet!', exclaimed at a high-pitch: 'Yep, just grab yourself a wetsuit there... Sweet! And get yourself a helmet SweetSweet! And we'll be getting down the caves SWEET!'

Of course it wouldn't be a kiwi activity if it didn't involve some kind of adrenaline rush. Blackwater Tubing delivers this by jumping backwards off underground waterfalls. Sarah did not look pleased when this part of the tour was explained to her. The jumping backwards thing is apparently risky enough to warrant a practice run. Dressed in wetsuits and crash helmets, and carrying our inner tubes, we waddled to a nearby stream where each of our group took turns to jump in, make a big splash, then paddle with the current to the side to climb out. When it came to Sarah's turn however, the cold water clearly induced some kind of shock, causing her to forget how to paddle completely. She was quickly taken by the current and carried downstream past the point where we were meant to climb out. Heroically, I dived back into the river to grab her just before she disappeared from sight, and towed her to safety. This act would have been more impressive had our young guide Brad not then shouted to me 'just put your feet down mate!', at which point I realised the 'river' was only four feet deep.

Anyway, with Sarah less than encouraged by her practice run, we drove to the caves access point and descended into the bowels of the earth. I really enjoyed it. At points we had to lie face down on our inner tubes and float under huge slabs of rock with only a foot of breathing space, and in others the caves opened out into huge caverns where we rode our tubes at pace down torrents of water. The waterfall jumps were awesome, and not nearly as cold as the trial run – after half an hour in cold water we couldn't really feel much colder. I think it's fair to say Sarah didn't like the experience as much, but Brad did a great job in guiding her down safely, and she has conceded that it was worth it in the end when we reached the glow-worm caves and switched off our head torches. By each grabbing the feet of the person behind us, our entire group was able to float down the underground river in a huge chain, everyone staring up at the luminous green lights that plastered the ceiling.

From Brunei we took a short 6 hour bus ride back into Malaysian Borneo, crossing the border at Kuala Belait. I then spent 16 hours holed up in a hostel in Miri with the tail-end of a bout of food-poisoning, willing myself well in time for a tour to the Niah Caves that we had booked for the following morning. Sarah tells me she spent a lovely afternoon exploring the 'sights' (browsing the shops and getting a pedicure).

Aside from a mild fever virtually indistinguishable from my base-level of tropical sweatiness, the next morning I was good to go and we set off with our guide Ken west on the coastal road to the limestone cliffs of Niah.

The Niah Caves are the result of similar limestone rock formations to those we saw in Halong Bay in Vietnam – they're enormous humps of rock, big sore thumbs in an otherwise flat jungle landscape. In Halong Bay water still laps the base of these rocks, in Niah the sea has rolled back several miles leaving jungle and more palm oil plantations between the beach and the caves.

Niah and its big brother Mulu (another set of caves in Sarawak) housed some of the oldest recorded human settlements in the region. Inside the mouth of the Great Cave at Niah, 'modern' human skulls have been found in a highly organised burial ground that dates back 40,000 years – the oldest in the whole of S.E.Asia – as well as a series of very faded cave paintings of boats and monsters dated at 20,000 years old.

We strolled the 4km from the camp to the caves, protected from the rainforest by a raised wooden walkway, before climbing the wooden staircase up the face of the limestone cliff to the enormous cave entrance. Once inside the mouth of the Great Cave, sunlight quickly became a distant memory and our torch did little to penetrate the heavy darkness around us. Following our guide's heels, we felt our way over damp wooden walkways deeper into the cave system. Only the clicks and screeches of bats and the echoes of dripping water gave us an idea of the scale of the space, until we rounded a corner and saw light lancing down from holes in the cave roof 50 metres above us.

Tourism in the Niah caves exists side by side with two older industries – guano (bat shit) farming and birds' nest collecting. Nitrate-rich guano from the 2-3 million bats living in the caves is shovelled up daily by groups of locals living in camps within the caves and sold as an expensive natural fertiliser. The ammonial stench hit us like waves in the more popular bat-caves. I've no idea how the farmers live with it day-in day-out.

Bird's nest collecting is a less disgusting but much higher-risk profession. Collectors ascend 100 foot high bamboo poles to knock down Swiftlet nests attached to the cave roof. The saliva that the birds use to construct their nests has supposed aphrodesiac properties that make them the most valuable ingredient in Chinese 'bird's nest soup'. It is this rich export market that causes otherwise sane locals to climb to such heights with no ropes.

Both these professions require their practioners to live in the caves in semi-permanent camps to guard their territories from interlopers. As we walked through the caves, we came across a guano farmer standing by the walkway on a rock in the milky half-light, smoking a cigarette and looking very much like an overgrown Golem – wearing only shorts and a non-functional head-lamp, he was skinny and pale with clammy-looking skin that stretched over a little pot belly. After our guide exchanged a few words with him ('Nice weather'?!?) we walked quickly on.

Fortunately we also managed a bit of escapism on a 3 day tour to Halong Bay, a beautiful archipelago of islands and islets (small islands, I discovered) to the east of Hanoi. We were a little nervous having booked our tour through the internet and heard a fair few horror stories about other people's experiences, but our fears proved to be unfounded. Our boat, the Dragon Pearl, was a gorgeous 2 storey craft, complete with a sun deck and newly-furnished rooms, and fresh seafood served at every meal.

During our 3 day tour, we visited the (literally translated) 'Amazing Caves', boasting stalagmites and stalagtites which have naturally formed into everything from buddhas to bears to giant 'happy sticks' (penises), and also went kayaking around some of the islands – which I am a lot better at now than I was 6 years ago, I must say! After this there was still plenty of time for sunning ourselves on the deck and swimming in crystal clear waters, with jellyfish (just about) far enough away not to pose a concern. James persuaded me to overcome my naturally nervous disposition and we jumped together off the top of the boat (sorry mum). It was a long way down but an exhilarating feeling!

We spent our first night sleeping on the boat and the next morning we woke ourselves up with an early morning swim in a deserted bay where we'd lain anchor overnight. If only every morning could be like this! We then sailed on towards Cat Ba island, with a stop at Monkey Island – a beautiful beach where we were the only people, yellow sand and clear blue water all that the eye could see. Thankfully the monkeys for which the island is named stayed beyond the treeline, content to lie in the shade while we burned ourselves to a crisp. Cat Ba island itself, where we stayed the second night, has unfortunately turned into a bit of a tourist trap, but we consoled ourselves in a few of the local bars with some super-cool Dutch guys from our group.

All in all a fantastic way to chill out after 2 months of hectic sightseeing, and a welcome relief from the intensity of Hanoi. We're looking forward to more little breaks like this over the next couple of months.