Without a doubt the most popular day trip out of Luang Prabang is the trip up the Mekong River to the caves at the mouth of the Ou river (hence the name 'Pak Ou' - 'mouth of the ou'). Although you can make most of the trip by road, boat is the best way to go even though it does take nearly an hour (or more if the river is low) to make the trip up river.
As you head up the Mekong from Luang Prabang, the limestone hills get higher, with sometimes sheer cliffs jutting straight up out of the water. On the bank opposite the point where the Ou River joins the Mekong, a large cave gapes open in the face of one of these cliffs.
The cave has been used for centuries as a repository for old or disfigured Buddha images. Even before Buddhism, the cave was believed to be a place occupied by spirits. You enter cave from the river - meaning that even if you make the trip by road, you have to use a boat to cross the river.
A path from the main cave (called 'Tham Ting' in Lao) leads around and up the hill to another cave, home to even more Buddha images. The upper cave is protected by a massive wooden gate. Inside, there are the remains of platforms and other structures. There are also many drawings on the walls.
A trip to Pak Ou typically includes a stop at the 'whiskey village' about halfway there. The proper name of the village is Ban Xang Hai, but everyone knows it as the whiskey village. Here whiskey is made from fermented rice soaked in water from the Mekong River. You can of course sample the wares as well as purchase a bottle. There's also a silk weaving village on the way.
If you time it right, starting off in the morning, you'll finish about noon and can have lunch at the village opposite the caves. There are of course several places in the village to satisfy your cravings.
Admission Fee & Getting There
There is an entrance fee of 20,000 Kips (US $2) to visit the Pak Ou Caves. Boat trips to the caves are usually around 80,000 Kip per person, or 300,000 per boat. While the rates are often posted, they are generally negotiable.