Son Doong Cave, Show cave in Quảng Bình, Vietnam

Son Doong is a natural cave formation in Quảng Bình in central Vietnam. The underground passages run for more than 9 kilometers through massive limestone rock, with the main gallery reaching over 200 meters in height and 150 meters in width in some sections.

A local resident named Ho Khanh came across the cave entrance in 1991 while searching the jungle for agarwood. British researchers conducted the first full exploration only in 2009, mapping the entire extent of the underground chambers.

The name combines the Vietnamese word "sơn" (mountain) with Đoòng, a Vân Kiều village near the entrance, so it means "cave of the mountain behind Đoòng". Hồ Khanh first named it Hang Hồ Khanh after himself, and the British Cave Research Association later asked to rename it Sơn Đoòng. Near the entrance lies the Vân Kiều hamlet of Bản Đoòng.

Visits require a permit and take place only with authorized guides from Oxalis Adventure Tours, as the cave sits within a protected national park. Expeditions run from January through August, before the rainy season begins and underground rivers make access impossible.

The two ceiling collapses are called dolines; the Vietnamese article names one of the forested chambers inside them "Adam's Garden". Sunlight through these openings lets a tropical forest grow on the cave floor, and the same passages hold fossil animal remains and coral-like formations.