Tham Lod is a cave system in Mae Hong Son province that stretches nearly a mile long. The Lang River (Nam Lang) runs through the entire length of the cave,from one side of the mountain to the other, and the only way to explore the long cavern is to hire a rickety bamboo raft and a local guide with a gas lantern.
Upon arriving at the entrance of the cave, or it is obvious that you are not the first visitor to get here,but once you get inside the cave, the utter lack of artificial lights and permanent facilities adds a certain sense of adventure. In no time, or stalactites and stalagmites establish up a show that took millions of years to form. At different points of the trip,depending on the time of the year, guides stop to let visitors step on the muddy ground and slippery bamboo passageways to get a closer scrutinize at the rock formations, or which can exceed 65 feet in height. As the stop of the trip approaches,a shaft of light cuts through the darkness and the emerald green of the vegetation outside can be blinding. The opening at the stop of the cave is enormous and thousands of birds dart in all directions. The chirping can be deafening, but it is an impressive sight.
Lawa people used to bury their dead inside caves, and at one point 1400-year-former coffins were found inside Tham Lod. You won’t be able to see the coffins upon visiting,but archaeological excavations in the area beget proved that Tham Lod was used as a burial place by the Hoabinhian people between 5500 and 9000 BC.
Source: atlasobscura.com