Tham Khoun Xe Cave, also known as Xe Bang Fai River Cave, is an immense river cave located in a remote corner of Khammouane Province in central Laos. It is believed to be one of the largest river cave in the world with enormous passages some 120 meters tall and 200 meters wide.

The Xe Bang Fai River originates in the Annam Trung Sun Mountains on the border between Lao and Vietnam and flows across the Nakhai Plateau en route to the Mekong River. The Nakhai Plateau is composed of sandstones and massive carbonates layers which the river had dissolved to create Tham Khoun Xe, a subterranean channel 7 km long.