Which cave in Vietnam contains the world's largest known cave passage by volume?

The Vietnamese cave containing the world’s largest known cave passage by volume is Hang Sơn Đoòng.

Also called Sơn Đoòng Cave, it lies in Phong Nha–Kẻ Bàng National Park near Vietnam’s border with Laos. The main passage is about 9 kilometers long, with sections roughly 200 meters high and 150 meters wide. Its enormous cross-section gives it the greatest known passage volume of any cave.

Local man Hồ Khanh found the entrance in 1990 while searching for agarwood, but he later lost track of its location. He rediscovered it in 2008, and a British Cave Research Association expedition surveyed the cave in 2009. Explorers eventually passed the imposing 60-meter Great Wall of Vietnam inside the cave.

Sơn Đoòng is a limestone solution cave formed over an estimated two to five million years. Collapsed ceiling sections, called dolines, allow sunlight into parts of the passage, where forests and other vegetation can grow. It is often confused with Malaysia’s Deer Cave, which has a very large entrance but a smaller passage volume.