Located in the northern part of central Vietnam, Phong Nha Cave is the second largest cave in the country and a UNESCO World Heritage Site. Phong Nha is surrounded by Phong Nha Ke Bang National Park. The park has nearly 300 caves, though only a fraction have been surveyed in any detail. Despite the existence of such a vast underground network, tourists are permitted only in the first mile or so of Phong Nha’s tunnels.