The Phong Nha Nature Reserve is situated on the edge of the Phong Nha/Ke Bang Karst plateau in central Viet Nam. It is only part of the total plateau, which extends to and adjoins the Hin Namno karst of the Lao PDR. Phong Nha contains many large and spectacular caves. The karst landscape is an extremely complex and ancient one, with high geodiversity and some geomorphic features of considerable significance. It has an Earth crust development history from the Ordovician period (464 million years ago)