One of the largest caves in the world, and certainly the largest in Vietnam, is Hang Son Doong. Approximately three million years old, Hang Son Doong Cave is an incredible destination unlike anywhere else on the planet. The cave is enormous, and it is possible for dozens of people to camp within it at a time. Bright blue water pools are located in the cave, and a river runs through it. Lush greenery lines the walls, thanks to erosion that lets in beams of sunlight. The cave is ethereal, and guided tours are available to best explore this amazing landmark.