Laos is the only landlocked country in Southeast Asia. The country is slightly smaller than Romania and Colorado. The landscape is mostly rugged mountains. The highest point is Phou Bia at . The Mekong River forms the border with Thailand. The mountains of the Annamite Range form the eastern border with Vietnam. The climate is tropical. The rainy season is from May to November. The dry season is from December to April. Laos has three seasons (rainy, cold and hot). The capital and largest city is Vientiane.