From the World Heritage inscription:
Luang Prabang is an outstanding example of the fusion of traditional architecture and Lao urban structures with those built by the European colonial authorities in the 19th and 20th centuries. Its unique, remarkably well-preserved townscape illustrates a key stage in the blending of these two distinct cultural traditions.
Prior to the communist takeover in Laos, Luang Prabang was the royal capital of the country. It is a very sleepy town (well, all of Laos is) on the Mekong river which is becoming a popular attraction on the tourist circuit in SE Asia. In addition to the European style colonial buildings, there are also several Buddhist temples in the area.
One of the most interesting things you’ll see in Luang Prabang is the daily alms ceremony. Every morning at sunrise, the monks of the local temples line up and walk through the streets of town to get rice and food from the locals. If you wake up early, you can buy some sticky rice and fruit and line up to give something to the monks. The Korean and Japanese tourists took it much more seriously than the Western tourists did.