Sai Yok National Park is a national park in Sai Yok district, Kanchanaburi Province, Thailand. The park, home to mountains, waterfalls and caves, is part of the Western Forest Complex protected area.
Within the park are remains of a bridge on the Burma Railway and of a camp used by Japanese troops during World War II. In 1978, the Russian roulette scenes of the film The Deer Hunter were filmed in the park. On 27 October 1980, Sai Yok became Thailand's 11th national park.
The park's major attractions are its waterfalls, including Sai Yok Yai waterfall which flows into the Khwae Noi river. Sai Yok Yai Lek waterfall lies south of Sai Yok Yai along the Khwae Noi.
The park also contains numerous caves, the largest of which is Tham Lawa with a length of 500 metres (1,600 ft). This cave complex consists of five large caverns, each containing large stalactites and stalagmites. Another cave system, Tham Daowadueng, is 100 metres (330 ft) long and was discovered in 1972. Tham Daowadung consists of eight chambers of stalactites and stalagmites.
Sai Yok's forest is primarily teak forest. During the Japanese occupation of Thailand, teak trees were felled for use as railway sleepers on the Burma Railway. The teak forest was replanted in 1954.
Animal species include elephants, tiger, barking deer, sambar deer, wild pig, gibbon, Malayan porcupine, slow loris and serow. A species of crab—the Rachinee crab, coloured red, white and blue—was discovered in the park in 1983. Sai Yok is home to Kitti's hog-nosed bat, a rare bat species considered to be the world's smallest mammal (weighing around 2 grams). The bat was first spotted in 1973 and is found only in some limestone caves of the park (including Tham Kang Kao) and surrounding areas in Kanchanaburi Province and nearby Myanmar.

Source: Wikipedia