“Phong Nha is a speleologists’ heaven on earth,” proclaims Lonely Planet. It contains “the oldest karst mountains in Asia, formed approximately 400 million years ago,” and is “riddled with hundreds of cave systems -- many of extraordinary scale and length -- and spectacular underground rivers.”
It’s full of caves. The “beautiful” Phong Nha Cave, which only accessible by dragon boat from Phong Nha town, explains Rough Guides. Dark Cave (Hang Toi) “involves a zip line, a muddy exploration, a cold swim and a short kayak trip.” Paradise Cave (Durong) “is the only cave in Phong Nha that can be explored without an arranged tour,” says Big World Small Budget. “Once inside the cave, gasp at the beauty as your eyes adjust and descend down the stairs into the darkness … an easy 1km stroll along a boardwalk exposes some of the most breathtaking stalactites and stalagmites in the park.”
The park features “great geological diversity and offers spectacular phenomena,” explains UNESCO. Inscribed on the World Heritage List in 2003, and covering 126,236 hectares, it “harbours a high level of biodiversity and many endemic species” in a landscape formed by “limestone plateaux and tropical forests.” It shares a boundary with the Hin Namno Nature Reserve in Laos.