The Centre of Laos consists some provinces Borikhamxai, Paksane Thakheh, Kammouane and Savannakhet. The Annamite chain extends north-south along the eastern part of this set, plains bordering the Mekong River forms the western part, in the center stood a few powerful massive limestones. It is accessed from the Vietnam Centre or from Vientiane or Pakse. North of Borikhamxai, travelers can explore the scenic limestone massif Phu Phu Man, near the valley of the Nam Hi and caves of Tham Konglor; further south, near Thakhek, old pagodas, Tham Xang and Tam Xienglieng other massive carved concavities. In Khammouane province, he discovers the Nam Theun, a huge artificial lake not lacking charm, along the Vietnamese border, the National Park Nakai Nam Theun and its vast mountainous jungles, along the N 13, across the Mekong, Savannakhet and colonial architecture.