What is the largest cave by volume in the world?

The largest cave by volume in the world is Son Doong, also called Hang Sơn Đoòng, in Vietnam. It is regarded as the largest known natural cave passage by volume.

Son Doong lies inside Phong Nha-Ke Bang National Park and contains a fast-flowing underground river. Its main passage is about 9 kilometres long, with sections reaching roughly 200 metres high and 150 metres wide. The surveyed volume has been estimated at about 38.4 million cubic metres, making the cavern large enough for striking comparisons with city blocks and aircraft.

The cave entrance was found in 1990 by local forest hunter Ho Khanh, but the cave was not fully explored and surveyed by a British-Vietnamese team until 2009. It formed in soluble limestone over millions of years. Collapsed sections of its roof, called dolines, allow sunlight into the interior, where trees and other vegetation grow underground.

The wording matters: Son Doong is the largest known cave passage by volume, not necessarily the longest cave or the deepest cave. Mammoth Cave is famous for its mapped length, while Jewel Cave and Carlsbad Cavern are different records altogether.