Designated a Unesco World Heritage Site in 2003, the remarkable Phong Nha-Ke Bang National Park contains the oldest karst mountains in Asia, formed approximately 400 million years ago. Riddled with hundreds of cave systems – many of extraordinary scale and length – and spectacular underground rivers, Phong Nha is a speleologists’ heaven on earth.
The Phong Nha region is changing fast. Son Trach town (population 3000) is the main centre, with an ATM, a growing range of accommodation and eating options, and improving transport links with other parts of central Vietnam.
The caves are the region's absolute highlights, but the above-ground attractions of forest trekking, the area's war history, and rural mountain biking mean it deserves a stay of around three days.