Hang Son Doong Cave, Phong Nha-Ke Bang National Park, Bo Trach District, Quang Binh Province, Vietnam

The cave was found by a local man named Hồ-Khanh in 1991. The local jungle men were afraid of the cave for the whistling sound it makes from the underground river. However, not until 2009 was it made known to the public when a group of British scientists from the British Cave Research Association, led by Howard and Deb Limbert, conducted a survey in Phong Nha-Ke Bang from April 10-14, 2009. Their progress was stopped by a large calcite wall. According to Limbert, this cave is five times larger than the Phong Nha cave, previously considered the biggest cave in Vietnam. 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.
Phong Nha Cave
Phong Nha Cave is also a cave in Phong Nha-Ke Bang National Park, a UNESCO World Heritage Site in Quang Binh Province, Vietnam. It is 7729 meters long and contains 14 grottos, as well as a 13,969 meter underground river. While scientists have surveyed it to a depth of 44.5 kilometers, tourists are only allowed to explore the first 1500 meters. It is the second biggest cave in Vietnam. Before discovery and exploration of Thien Duong Cave, Phong Nha Cave was considered the most beautiful cave in Vietnam.