Sai Yok National Park

Stone Age traces have been found here. King Chulalongkorn first visited Sai Yok in 1877 and again in 1888, writing an account of the journey and naming Phra That Loi cave; Sai Yok Yai Falls was once called Khao Chon Falls. The song 'Khmer Sai Yok', composed by Prince Naris from an old lullaby melody to evoke the road to Sai Yok, was first performed at the King's birthday celebration on 20 September 1888.

In 1942–45 the Death Railway ran through the area and the Japanese army camped here — stoves and bridge piers remain. Dawadung cave was found in 1972, and in 1973 Kitti Thonglongya discovered Kitti's hog-nosed bat, weighing about 2 g with a 10 cm wingspan and often called the world's smallest mammal. The park was declared Thailand's 19th national park on 27 October 1980.

Sai Yok Yai Falls drops about 10 m straight into the Khwae Noi, best seen from the suspension bridge by the visitor centre, with the strongest flow July–November; Sai Yok Lek is about 300 m away. Lawa cave, the park's largest at about 500 m with five chambers, is reached by longtail from the raft houses; Dawadung cave has eight chambers, about 6 km upriver then 1.5 km on foot. Sai Yok Noi Falls lies about 30 km south, outside the park.

It opens roughly 08:00–16:30. Fees: Thais 60/30, foreigners 300/150, cars 30 baht. There are park bungalows (800–3,000 baht) and a campsite, and private raft houses on the Khwae Noi offer longtail trips at about 400–500 baht per half hour. A fire destroyed 14 raft rooms on 29 January 2023, so choose rafts with fire equipment, and wear life jackets on boats as the current is strong. Wild elephants roam the area, some caves close in the rains, and pets are not allowed.