The Mekong is Southeast Asia’s greatest river with an estimated length of 4,350 km (2,703 miles). Laos actually has the greatest share of the Mekong River. With few good roads and mountainous terrain, the river is Laos’ principal transportation. The Upper Mekong in Laos is considered one of the most stunning journeys of the entire river. A great way to enjoy the scenery is a boat trip from Huay Xai at the border with northern Thailand to Luang Prabang, or vice versa.