Getting from Thailand to Vietnam

Susan Smillie relaxing in a hammock on Rabbit Island, Cambodia. Photograph: Lisa Vander Meulen. Click on the magnifying glass icon for a landscape shot of the area

I've been sitting still for an hour, watching, listening, in the dark. Macaques swing through the cliff-top trees opposite, the drilling of cicadas has begun. Frogs take up the chorus below, the river rushes ahead, gibbons whoop in the distance. Even the leaves are noisy, falling around the deck of my beautiful treehouse with a thud. Stars appear to rush towards me; fireflies twinkling in the Takian trees.

I'm staying at Our Jungle House in Khao Sok – Thailand's largest national park, near Phuket. Run by social entrepreneur Bodhi Garrett, it's a model of ecotourism but doesn't shout about it. What you see is tasteful accommodation, all soft lighting and wood carvings while, in the background, they're quietly building schools and developing community-based tourism projects.

I took a group tour to Cheow Larn lake with Por, a young local guide, and we ventured north, three hours by longtail boat to Klong Saeg Wildlife Sanctuary, leaving the rest of the tourists behind. It's magical and remote, mist drifting over the jutting limestone karsts, the lake banked by thick jungle. We hiked up wild elephant trails, followed bear tracks, explored lakeside caves and ate fish caught beside the bamboo rafthouses we would sleep in. Before bed, Por took us on a night safari where we floated silently past shy gaur – tragically, the heads of these endangered bison can earn poachers £2, 000 apiece.

Magical and remote … Cheow Larn lake

It was all a far cry from where I started the year. January blues were abetted by minor heartbreak and I planned a healing trip to Thailand, Cambodia and Vietnam. So far, so cliched. Friends, recalling youthful travels, promised adventure. Contemplating my more mature 41 years, I privately worried at the prospect of travelling among twenty-somethings headed for full-moon parties. Instead, I booked into a yoga centre on Koh Phangnan. I would emerge serene and calm, I told surprised friends. Arriving at the retreat, I passed men chanting among – or perhaps to – the trees. In a temple, strangers discussed receptivity to love and offered to partner me in tantric workshops. Sitting on the resort's beach, I pondered my situation when the faint strain of bongos made a decision easy. I beat a hasty retreat.

Several hours later, I was on the neighbouring island, enrolling on an open-water dive course at family-run Master Divers. Koh Tao is a diving epicentre and, as a result, the main town, Mae Haad, is also a backpacker's haven, its narrow pathways and rising streets crammed with budget accommodation. A basic, clean beach bungalow at Ananda Villas costs £23 a night (rooms start at £10) and, as with much of Thailand, there's excellent affordable food everywhere. Master Divers are keen environmentalists so, at lunchtimes, I used their reusable plastic containers to fill with fresh papaya salads and spicy noodle soups from nearby street stalls. Mornings were spent in the classroom, afternoons in the sea in small groups, under the expert guidance of Simone, a charming German divemaster.

We got to grips with the basics at one of the most scenic sites, Japanese Gardens. It's ideal for learners and snorkellers, with the reef across the bay going from paddling depth to 14m, vibrant soft and hard corals, and a wide variety of fish: wrasses, parrotfish, titan triggerfish. Once we'd mastered safety techniques, Simone led the way as we glided past lobed pore coral heads fully five metres high, and fields of slipper corals. It wasn't long before we stumbled upon a hungry turtle, chomping away, unperturbed by the captivated audience of divers: you can see why people flock here to learn to dive.

I was smitten, and this newfound passion saw me heading, freshly qualified, to Khao Lak for a liveaboard trip to the Similan islands with an underwater camera. Happy days were spent launching myself into the deep from Sea Dragon's dive boat, photographing turtles, barracuda and stingrays, and using up my air trying to outswim tuna. We were the first divers to visit the East of Eden site, reopened after two years, and here I got up close, too close, to a giant moray eel I later discovered was almost certainly Scarface – a known resident of the table coral at 16m depth, and infamous for having bitten a diver's thumb off. Evenings were passed swapping stories and pictures with other divers over the Thai kitchen crew's fragrant curries.

Diving in … a hungry turtle spotted on the Master Divers trip

The only time I felt "older" was on the backpacker bus trail from Koh Tao to Khao Sok, where some studiously jaded youngsters viewed my cheery optimism with the contempt it obviously deserved. "God, Thailand's so slow, " they whined, even as the bus company sent a car to reunite the ingrates with a forgotten backpack. Not all youthful backpackers are cast from the same mould. In Koh Tao, I had great fun with a trio of twenty-somethings from Paris, and Khao Sok was memorable for the stunning scenery and wild animals, as well as for sharing those experiences with other travellers. I set off for Phnom Penh, happy I'd made lifelong friends.