The Pak Ou Caves are upriver from Luang Prabang at the confluence of the Mekong and the Nam Ou rivers. Legend maintains that King Setthathirat discovered these two caves in the 16th century CE, and they have been venerated ever since. Both caves are full of Buddha images, some of venerable age. Luang Prabang was formerly the capital of a kingdom of the same name. Until the communist takeover in 1975, it was the royal capital and seat of government of the Kingdom of Laos. The city is nowadays a UNESCO World Heritage Site.