Son Doong cave is a cave in Phong Nha-Ke Bang National Park, Bo Trach District, Quang Binh Province, Vietnam. It has a large fast-flowing underground river inside. The biggest chamber of Son Doong is over five kilometers in length, 200 meters high and 150 meters wide. With these dimensions, Son Doong overtakes Deer Cave in Malaysia to take the title of the world's largest cave.[news.ifeng.com]