Khao Sok, a lake of limestone islands in the rainforest

Most travellers cross southern Thailand on the way from one coast to the other, from the Gulf islands of Koh Samui and Koh Phangan to the Andaman beaches of Krabi and Phuket. Between the two, in the mountainous spine of the peninsula, lies one of the country's finest wild places. Khao Sok National Park protects a large area of lowland rainforest, limestone mountains and rivers. Together with neighbouring reserves, it forms one of the biggest blocks of forest in southern Thailand. The forest is often described as among the oldest evergreen rainforests in the world, and it is rich in wildlife, though much of it is shy and hard to see in the dense green.

The lake

At the heart of the park is Cheow Lan Lake, which was made, not found. In the 1980s the Ratchaprapha Dam was built across the Klong Saeng river to generate electricity, and the valley behind it flooded. The water rose around the limestone peaks, turning them into islands and cliffs that rise sheer from the lake, some of them hundreds of metres high. Their sides are draped in forest and creepers, and the water at their feet is a deep, still emerald.

The best way to see the lake is by boat. Long-tail boats carry visitors between the peaks and along narrow arms of the lake into the forest. Several floating raft houses, simple bungalows built on bamboo rafts moored in quiet coves, give the chance to spend a night on the water. Waking on the lake at dawn, with mist lying on the water and the calls of gibbons echoing from the forest, is the memory that tends to stay.

There are also caves to explore in the limestone, some with streams flowing through them that have to be waded or swum. These should only be visited with a guide, and never in heavy rain, when water levels can rise quickly.

The forest and its wildlife

Khao Sok's forest is home to an extraordinary range of animals and plants. Gibbons, macaques and langurs live in the canopy. Hornbills, with their huge curved bills, are among the most striking birds, and the sound of their wings is often heard before they are seen. Elephants, tapirs, bears and even tigers still live in the wider area, though they are very rarely seen. The park is also known for the rafflesia, a parasitic plant with one of the largest flowers in the world, a huge, fleshy, reddish bloom that smells of rotting meat to attract flies. It flowers briefly, mainly in the cooler months, and finding one is a matter of luck and a good guide.

Guided walks in the forest, river trips by canoe or inner tube, and night safaris to see insects, frogs and nocturnal animals are all popular around the village at the park's main entrance.

The dam that made the lake also displaced the villages that once stood in the valley, and their people were moved to new settlements nearby. Today many of the boatmen, guides and raft-house staff on the lake come from those communities, and tourism has become one of the main sources of work in the area. Choosing local guides and staying in locally run accommodation is the most direct way to see that the money from a visit stays where it is needed.

When to go, and how

The park lies in the path of both monsoons and is wet for much of the year, which is why the forest is so green. The driest months are roughly from December to April, when walking is easiest. In the rainy months the forest is at its lushest, but trails are muddy, leeches are common and some activities may be cancelled.

Explore Worldwide's Family Thailand: River Kwai and Islands, thirteen nights, is designed for families. It includes Khao Sok National Park and Cheow Lan Lake, along with Bangkok, Ayutthaya, Kanchanaburi and Sai Yok National Park, and the islands of Koh Phangan and Koh Samui.

Explore Worldwide's Discover Thailand, eleven nights, includes Khao Sok on a route that also takes in Bangkok, Kanchanaburi and Hellfire Pass, Phetchaburi and Pranburi on the Gulf coast, Koh Lanta and Krabi.

Khao Sok is a reminder of what much of southern Thailand looked like before roads, plantations and resorts, and a fine counterpoint to time on the beach.