Phong Nha-Ke Bang National Park and Hin Nam No National Park

Asia's oldest great karst landscape began forming some 400 million years ago, and today it spans the Viet Nam-Laos border as a wilderness of jagged peaks, sinkholes and underground rivers, with more than 220 kilometres of caves documented so far — among them passages ranking with the largest on Earth. Rare and endemic species inhabit forests from dry karst heights to moist lowland jungle. Phong Nha-Ke Bang was inscribed by UNESCO in 2003, and the World Heritage Site now reaches across the border into Laos's Hin Nam No National Park.