Khao Sok shelters a rainforest often reckoned at around 160 million years old — older, by that measure, than the Amazon. At its heart lies Cheow Lan Lake, which is younger than many of the people who visit it. The water appeared in 1987, when the Ratchaprapha Dam flooded a forested valley for hydroelectric power. As the reservoir rose it drowned the lower hills and left their limestone summits standing alone. More than a hundred karst towers now climb straight out of the emerald surface, the tallest ridge in the park reaching 960 metres. Three of them, leaning together near the dam wall, are known as the Three Brothers and mark the first stop of almost every boat. Forested to their peaks and doubled by their reflections, they have earned the lake constant comparison to Guilin in China.
The lake shows its best to those who stay the night in one of the floating bamboo bungalows tethered to the foot of the cliffs. Before dawn the water falls silent, mist settles into the gaps between the peaks, and the whooping calls of gibbons carry across the valley from the forest. As the sun climbs, the mist thins and the surface turns to a blue-green mirror you can cross by canoe, gliding beneath rock walls hundreds of metres tall. The surrounding forest still holds wild elephants, tigers, hornbills and the giant Rafflesia flower, though most stay hidden and a sighting is a matter of luck. Khao Sok is a protected national park with no road along the lake, so the only ways to see it are by longtail boat from Ratchaprapha pier or from a raft house moored beneath the cliffs.