Phong Nha-Ke Bang National Park (Vietnam)

With jagged hills draped in a shroud of rainforest and mountain rivers charging through plunging ravines, Phong Nha-Ke Bang is one of Vietnam’s most spectacular national parks, even just counting the area above ground. Things get even more dramatic when you crawl underground to the reserve's twisting and turning cave systems. The cathedral-like chambers of Hang Son Doong, the world’s largest cave, are only open to expensive caving tours, but more accessible are the ziplining and kayaking thrills of Hang Toi (Dark Cave), and the ethereal beauty of aptly named Paradise Cave.