Twenty five kilometres away from Luang Prabang, opposite the mouth of the Nam Ou River, are the Pak Ou caves. There are two caves Tham Thing (the lower cave) and Tham Phoum (the upper cave).

These caves contain thousands of Buddha images and are of great religious importance to the Theravada Buddhists in Laos. These caves were converted into Buddhist temples in the 15th century and are used as a site for old Buddha images that can no longer be venerated in a temple, either because they are damaged or the temple they were displayed in has been destroyed.

At Laos New Year, pilgrimages of Lao people go by boat to the caves and perform the washing ceremony of all the old Buddha images. Previously this was performed by the King and members of the Royal Family but now is performed by the Governor of Luang Prabang and local families.