Son Doong cave (Vietnamese: Hang Son Doong) is the world's largest cave, located in Quang Binh province, Vietnam. It is found by a local man named Ho Khanh in 1991 and was recently discovered in 2009 by British cavers, led by Howard Limbert. The name "Son Doong" cave means "mountain river cave", It was created 2-5 million years ago by river water eroding away the limestone underneath the mountain Where the limestone was weak, the ceiling collapsed creating huge skylights.
Formed in Carboniferous/Permian limestone, the main Son Doong cave passage is the largest known cave passage in the world by volume – 38.4x106 cubic metres, according to Howard Limbert. It is more than 5 kilometres (3.1 mi) long, 200 metres (660 ft) high and 150 metres (490 ft) wide. Its cross-section is believed to be twice that of the next largest passage, in Deer Cave, Malaysia. The cave runs for approximately 9 kilometres (5.6 mi) and is punctuated by 2 large dolines, which are areas where the ceiling of the cave has collapsed. The dolines allow sunlight to enter sections of the cave, resulting in the growth of trees as well as other vegetation.
By mid-2019, it became clear that the cave is connected by its underground river with a nearby cave called Hang Thung. This increases the effective volume of the cave by more than 1.6 million cubic metres.