Nature carved the Pak Ou Caves inside a limestone cliff called Pha Hen at the water’s edge of two rivers: the Mekong and the Nam Ou. This is the opening of the lower cave called Tham Ting. Inside its dark crevices are thousands of Buddha statues that have been donated by local villagers. If you are adventurous, you can also walk up the steep staircase to the second cave called Tham Theung. However, it is a tough climb and very dark once you arrive.