These caves in the rocky walls of the sandstone mountains at the confluence of the Ou river and the Mekong, some 25 kilometres upriver from Luang Prabang, are the most important attraction out of town.

The caves are inhabited by thousands of Buddha statues, some allegedly more than 300 years old. Monks used to live in the caves, too. When Laos was still a monarchy, the caves were visited every year by the king. A small royal Wat is near the caves.

The citizens of Luang Prabang believe that many good-natured spirits have their homes in the caves. Thus they undertake short pilgrimages there on special occasions, especially traditional New Year's Day. The best way to visit the caves is by boat tour. The nature along the Mekong is absolutely beautiful, and a boat tour to Pak Ou is likely to be the most commemorable excursion from Luang Prabang.