Phong Nha Cave

Phong Nha Cave (Động Phong Nha, Vietnamese pronunciation: [ɗôŋ͡mˀ fɔ̄ŋ ɲā]) is a cave in Phong Nha-Kẻ Bàng National Park, a UNESCO World Heritage Site in Quảng Trị Province, Vietnam. It is 7,729 meters long and contains 14 grottoes, as well as a 13,969 meter underground river. While scientists have surveyed 44.5 kilometers of passages, tourists are only allowed to explore the first 1500 meters.