Huay Xai (also Houayxay) is the capital of the Laos province of Boko. It lies on the banks of the Mekong river, which forms the border to Thailand. More or less a transport stop-over, there is not much to see in the small town.
Huay Xai is a popular border crossing between Laos and Chiang Khong in Thailand, the only one in the north. Once a big opium producing centre for the Americans during the war, the town itself is now of interest only as a border crossing point.
The town has a number of guesthouses and restaurants which adequately cater to tourists' tastes. Many have information about travelling through northern Laos, as well as selling boat and bus tickets.
There is not a lot to do in Huay Xai. Fort Carnot on the hill, which was built to house the French Foreign Legion, is now a Lao Army barracks and visitors are not welcome, while there is a wat in the centre of town which is nice enough but only worth a visit if you are particularly curious about temples. A couple of travel agencies in town offer day trips visiting local ethnic minority villages. Most people just stay overnight and move on.
The majority of travellers crossing into Laos at Huay Xai head down the Mekong River to Luang Prabang via Pak Beng, and this journey is a major highlight of any trip to Laos. Many people choose to stay overnight in Chiang Khong on the Thai side but Huay Xai is a charming place to at least spend the night. It is also a good place to ease yourself into Laos, particularly if Pak Beng is to be your next stop.