In complete darkness, lying on my back, the only thing I can hear (apart from my pounding heart) seems to be the sound of air being slowly let out of a tyre ... phhhhhssss. But there are no tyres here, deep in the caves of Koh Panak, a tiny island 20km north-east of Phuket, southern Thailand. In fact, the only inflatable thing for miles around is the kayak keeping me afloat, so surely that hissing sound can't be good?
No point asking the "sea captain" paddling the boat as he speaks only Thai, but we're definitely losing air and getting lower and lower in the water.
Scrape, scrape goes the rubberised kayak as it is somehow squeezed under an impossibly small gap in the cave system, finally rounding a bend and revealing a hint of light somewhere ahead.
At last the penny drops (as does the rate of my heart) and the reason for inflatable kayaks suddenly becomes clear. Perhaps they should call them deflatable kayaks - without that particular ability, we'd be stuck deep in these amazing sea caves.
Depending on the height of the tide the kayak can be gradually deflated to sink us down, just enough to make it through the narrowest of gaps and eventually bring us out into the hidden centre of the island.
Emerging from the blackness of the caves we enter an incredible lagoon, completely surrounded by 30m high vertical limestone cliffs. The water is calm, mangroves sprout up haphazardly and there is virtually no sound other than the gentle splash of paddles breaking the water's surface. It's a tranquil, magical place, which we paddle around for 10 minutes before it comes time to lie back and squeeze our way through another black tunnel. We emerge five minutes later to the outside world where the swell of the open sea is a shock after the calm waters inside the lagoon.
Back on board the speedboat that brought my group here from Phuket Boat Lagoon, we are soon racing north for our next stop of the day, Koh Panyi Muslim fishing village. Almost the entire village sits on stilts over the sea, although its mosque is built on solid ground nestled alongside the steep limestone cliffs that make up most of the island. As well as a school, there are numerous market stalls and restaurants, mostly catering to the tourist boats arriving en masse in time for lunch.
When the tourists aren't there the island's main livelihood is fishing. After a filling lunch of local fish and meat curries at one of the waterfront restaurants, it's time for a stroll around the narrow alleyways through the markets, past the houses and village school.
Along the way, as you pass hanging birdcages, food stalls and souvenirs, you are always aware of the sea just a few metres below the sometimes rickety boardwalks underfoot. Although many of the houses are pretty basic wooden huts on stilts, some have ornate doorways and patterned, tiled walls.
Children are everywhere, sometimes following visitors and trying to sell postcards. It's an interesting village, but it seems hard to imagine it surviving without the lunchtime tourist boats keeping the restaurants and markets in business.
The rest of day at sea is spent speeding past many stunning islands in this part of the Andaman Sea, stopping at a few to swim, snorkel or just sunbathe on secluded beaches. Many of the day-long speedboat tours can be tailored to take in what you want to see, but most will take you Ko Phing Kan - more popularly called James Bond Island after it was used as a backdrop for the 1974 movie The Man With The Golden Gun.
Unless you're a huge James Bond fan, a visit to the island is not much more than an excuse to crowd ashore with other tourists, take some pictures and buy souvenirs. Even the isolated island of Koh Nakaya, where we stopped for a swim later in the day, didn't stay secluded for long as several other boats arrived, spilling throngs of beach-goers on to the previously deserted beach. But it was beautiful while it lasted.
Beaches are without doubt a major drawcard for many holidaymakers to Phuket, and with good reason - the island has kilometres of beautiful sandy beaches - but I was keen to find out what other attractions were on offer. One day we hired bikes and went for a ride inland from our beachside resort, through rolling hills, rubber plantations and small villages until we reached the nearby town of Thalang. Here we visited the Phra Nang Sang Temple where local school children studied and played in the cool, breezy courtyards among a mass of fluttering flags.
The shelter brought a welcome rest after the morning's 35 degree heat on our 10km bike ride - those conditions had already taken their toll on one of our group who had to be collected by van and returned to the resort to cool down after half an hour in the saddle. After a couple of hours of mostly gentle pedalling, taking in the scenery and pausing frequently for water breaks, we, too, elected to be picked up by the air-conditioned minivan and whisked back to the resort for lunch and an afternoon swim. Well, we didn't want to overdo it.
After a good rest, we were much better prepared for the next day's excursion up into the hills of Phuket, overlooking the southern tip of the island. Piling into a Land Rover, we're driven up into the high jungle for a meeting with one of Thailand's best-loved creatures - elephants.
Traditionally Thailand's elephants have been highly regarded and used for transportation and logging in the forest and jungle regions, but since a ban on the use of teak and other hardwoods came into effect, the elephants have been increasingly used for tourism. This change has not only helped to maintain the elephant population, it has even seen their numbers rise.
After being shown around a rubber plantation, watching a monkey being trained to pick coconuts and a demonstration of how to make a jungle curry paste, it's finally time to climb aboard my elephant, Yeera, for a half-hour stroll through the forest. With a strangely disconcerting rolling motion I'm off through the sun-dappled pathways of the high jungle.
The elephant driver seems happy enough, perched straight on Yeera's neck, using just his knees to keep his balance, while I've got a wooden bench seat, complete with safety bar to keep me in place, my feet dangling down against the elephant's back.
It does take a while to adjust to the lolling ride, especially down some of the steep tracks where you feel as if you could easily be pitched off with the next huge elephant step. But Yeera seems perfectly surefooted and at ease in these surroundings. The only injury I was likely to encounter was a twisted back from constantly turning round to take photos of the others in my group on their elephants bringing up the rear.
All this activity here on Phuket had, for the most part, kept me away from the island's renowned beaches. But by now I felt I'd earned a rest, so it was time to venture the 150m from my luxurious resort, Indigo Pearl, to discover the beauty of the adjoining Nai Yang Beach.
Early the next morning I'm the only one strolling the length of the beach just before sunrise, but I'm soon joined by a couple of locals who wade out into the shallows unfurling a fishing net between them before circling around in the hope of netting some red snapper.
Gradually a few more locals arrive, clamber aboard their fishing boats and head off out to sea. One woman starts to rake and sweep the sand between the deserted beach chairs and a lone dog follows me half-heartedly for a few minutes before curling up under a chair. Otherwise I have the beach to myself - just the way I like it. Later, in the heat of the afternoon, this particular stretch of beach in the Sirinat National Park is still surprisingly quiet. By the end of the day a few more tourists venture out to photograph the sun sinking smoothly over the horizon behind a line-up of deserted fishing boats.
Now if I could just find one of those inflatable kayaks, I could paddle off into that sunset.
Getting there: Thai Airways fly direct from Auckland to Bangkok four days a week. Connecting flights to Phuket are available.
Where to stay: The Indigo Pearl Resort is adjacent to the beautiful Nai Yang Beach & National Park.
The Diamond Cliff Resort & Spa at the northern end of Patong Beach.
Further information: See the Tourism Authority of Thailand website.
Martin Sykes travelled to Phuket courtesy of the Tourism Authority of Thailand and Thai Airways International.