The breathtaking limestone mountains that frame the Lao city of Vang Vieng are rugged by underground cave systems. Some of the caves are well developed with electric light and masonry steps; others must be explored by the light of the headlamp. Some caves are unbelievably large and are adorned with stalagmites and stalactites; some are so small that a human can barely squeeze through the tiny openings. Some are filled with water and can be explored by tube or kayak, others have served as temple sites for Buddhist believers for centuries.
Tham Nam is a highlight of the Cave Group near Vang Vieng. The cave is about 500m long, and a tributary of the Nam Song flows out of its low entrance. It is roughly 400m south of Tham Hoi, the village with the Elephant cave. The Water Cave seems to combine aspects from all the main attractions of Vang Vieng into an extraordinary experience: a cave, a river, and spectacular scenery. On a rope, you go about 500 meters through the cave on an underground river. The tunnel is narrow and very low, with sinister formations on the ceiling. Also, the water is not so deep, the darkness and disorientation create an exciting experience.