Turning off Rte 12 at Km 14 (before a major bridge) you'll come across a sign pointing to this cave. Follow the dirt track south for about 400m near the village of Ban Songkhone (about 10.5km from Rte 13), to the stunning limestone cave Tham Xieng Liap, the entrance of which is at the base of a dramatic 300m-high cliff.
The cave is about 200m long and, in the dry season, you can walk/wade through and swim in the picturesque valley on the far side. Paa faa (soft-shelled turtles) live in the cave, while the cliffs outside are said to be home to the recently discovered kan yoo (Laotian rock rat). In the wet season you'll need to rent a boat (30,000K) from the Xieng Liap bridge.