The Thung Yai Naresuan and Huay Kha Kaeng Reserves, as well as Khlong Lan and Mae Wong National Parks. Together, they form Thailand's largest wildlife haven and Southeast Asia's top virgin forest.

Thi Lo in the local language means waterfall and Su means loud, thus, Thi Lo Su means waterfall that makes a loud noise. This is due to its size and the intense flow of the stream. In Karen, "Thi Lo Su" means Black Waterfall.

The biggest and the most beautiful waterfall in Thailand, Namtok Thi Lo Su is also considered the sixth biggest waterfall in the world.

The waterfall itself originates from Huai Klotho, streaming along limestone cliffs at the height of 200-300 meters down to cascading tiers which are surrounded by intact natural forests.

There is a cave behind the waterfall worth exploring and several levels of pools for swimming. To get there, visitors can either raft or drive. For those deciding to drive a 4WD vehicle, the distance is 47 kilometers from Umphang to the wildlife sanctuary office. From there, visitors have to walk along the 1.5 kilometers self-guided forest trail which provides unrivalled natural forest scenery.

Please note that vehicles can possibly reach the office only during November to April. In the rainy season, Thi Lo Su is accessible only by rafting along Maenam Mae Klong. From the drop-off point, visitors have to continue on foot for approximately 4-5 hours.

Camping at the Wildlife Sanctuary Headquarters is allowed near the falls, especially during November December, when the waterfall is at its most beautiful. Visitors are advised to make enquiries with the TAT Office in Tak Province (Tel: 085 551 4341-3) regarding travel conditions and camping opportunities.