Khao Sok National Park

Listen first. Before anything else, let the sound of this place settle around you. There is the steady drone of cicadas, rising and falling like a slow machine. There is water somewhere, dripping from leaves or running over stones. The air is warm and heavy, and it smells of wet earth and green growth. Look up, and pale limestone cliffs rise straight out of the forest, streaked black and grey, with trees clinging to ledges where no tree should be able to grow.

This is Khao Sok National Park, in Surat Thani province in southern Thailand. You are standing near Ban Ta Khun, the district that holds the park's great reservoir and the dam that created it. Thailand declared this area a national park in 1980. Today it covers several hundred square kilometres of rainforest, rivers, caves and karst mountains. It sits roughly between the Andaman coast and the Gulf of Thailand, on the spine of the southern peninsula, and it catches heavy rain from both seas.

That rain explains much of what you see. This part of Thailand is one of the wettest in the country, and the forest here is evergreen. It stays green through the whole year. You will often hear a popular claim — that this rainforest is older than the Amazon. Guides and signs repeat it often. The idea is that this region kept a stable, warm, wet climate through very long periods of time, so the forest had an unusually long time to grow and diversify. Treat it as a well-loved story, not a precise measurement.

Now look again at those cliffs. They are limestone karst — rock formed from ancient sea life, then lifted, cracked and slowly dissolved by rainwater. Karst is the name for this kind of landscape, where water carves rock into towers, caves and sinkholes. The sharp peaks around you are what remains after a very long process of erosion. Inside many of them, water has opened caves. Some hold stalactites, bats and small streams that run in complete darkness.

Here is the first surprise for many visitors. Much of the water you may see from Ban Ta Khun is not a natural lake at all. Cheow Lan Lake is a reservoir. It formed when the Ratchaprapha Dam was built across a river valley in the 1980s to generate electricity. As the water rose, it flooded the valley floor. The limestone peaks that once stood above forested valleys now rise straight out of green water, like islands in a drowned landscape.

That flooding had a human cost. Villages stood in the valley before the dam, and families had to move to new land. Forest was submerged too. Some visitors on boat trips notice the grey trunks of dead trees still standing in shallow corners of the lake. They are quiet reminders of what lay here before. The reservoir is now the reason many people come, but it is worth remembering that this water covers someone's former home.

On the lake, you may see floating raft houses — simple bamboo or wooden huts resting on pontoons at the edges of the water. People stay overnight in them. In the early morning, mist often lies low over the surface, and the cliffs appear slowly as the sun climbs. Sounds travel far across still water. A boat engine can echo off the rock walls for a long time after it passes. In the evening, the calls from the forest grow louder again.

And those calls deserve attention. Khao Sok is home to a wide range of wildlife. Gibbons live in the canopy, and at dawn their whooping songs can carry across whole valleys. Hornbills — large birds with heavy, curved beaks — fly overhead with a loud rushing sound from their wings. Macaques are common near trails and rivers. Wild elephants, gaur, and even tigers have been recorded in the wider protected forest, but they are shy and rarely seen. Most visitors meet the smaller life instead.

Here is the second surprise. This forest is one of the places where you may find Rafflesia kerrii, one of the largest flowers in the world. It has no leaves and no stem that you would recognise. It lives as a parasite inside a jungle vine, and then a huge reddish-brown bloom appears on the forest floor. It does not smell sweet. It smells like rotting meat, which attracts the flies that pollinate it. It blooms only in certain seasons, and each flower lasts just a few days.

The forest also carries a more recent political story. In the 1970s, during a period of conflict in Thailand, communist insurgents and, later, some student activists took refuge in remote jungle areas, and Khao Sok was among them. The steep terrain and thick cover made it very hard to reach. Their presence is part of why the forest stayed less developed for a time. Today, that history is mostly invisible. What you see instead is the forest itself, which kept them hidden.

As you walk, notice the details at ground level. Look for buttress roots — wide, flat roots that flare out from the base of tall trees like the fins of a rocket. They help the trees stand in thin, wet soil. Look for rattan palms with sharp spines, and for strangler figs wrapped around older trees. Watch the trail edges for leeches after rain. They are harmless, but they are persistent, and they are a sign of how wet this forest truly is.

The Sok River runs near the park entrance area, clear in dry weather and brown and fast after storms. Many people float down it on inner tubes or travel along it by canoe, passing under hanging vines and limestone overhangs. Along the banks, you may see monitor lizards resting on logs, or kingfishers flashing blue over the water. The river is a gentler way to enter the forest than the lake, and it shows the park at a closer, more personal scale.

So pause for a moment where you stand. Feel the humidity on your skin. Look at the colour of the rock, the many shades of green, the light falling through gaps in the canopy. Listen for one sound you have not noticed yet — a bird, a branch, a drop of water. When you walk on, take that sound with you. This forest has been here for a very long time, and it will keep growing quietly after you leave.