Khao Sok is an ancient rainforest in southern Thailand wrapped around a lake that is younger than most of the people on it. The reservoir was filled in 1987, and the water rose until only the tops of the limestone hills were left above it. So the hundred-odd towers standing out of Cheow Lan Lake are summits, and the boat crosses them at what used to be halfway up a slope. There is no road along the shore. Every trip starts with a longtail from the Ratchaprapha pier, threading between cliffs that come up sheer from the water and double themselves on it. Near the dam the Three Brothers lean together, three sharp peaks that are the first landmark of almost every tour, and a canoe will take you right up to their forested feet.
The hour that matters is before sunrise. Mist fills the gaps between the peaks, the water goes flat, and the white-handed gibbons start. They pair for life and sing in duets, the female leading the loudest phrases, and the sound carries more than a kilometre through the canopy; you will hear them long before you see anything. Hornbills cross between the towers, macaques work the shoreline, and now and then elephants come down to drink. Walks from the water reach caves like Nam Talu and the Coral Cave, where you wade streams and squeeze past stalactites by torchlight, with the shells of an old tropical sea still in the walls. On the forest floor, between January and March, Rafflesia kerrii opens a rusty-red bloom up to eighty centimetres across. It has no leaves, stem or roots of its own, and smells of rotting meat to bring in the flies. You sleep in a bamboo hut rafted to the foot of a cliff, with the lake lapping under the floorboards and the drowned forest of that valley still down there in the dark.