Hang Sơn Đoòng

Hang Sơn Đoòng is a huge cave in Phong Nha–Kẻ Bàng National Park in central Vietnam, near the border with Laos. It has the largest known cave passage in the world, measured by volume, and a fast underground river runs through it.

The main passage is more than five kilometres long, about 200 metres high and 150 metres wide, and the whole cave runs for about nine kilometres. Where the roof has collapsed, sunlight pours in, and trees and other plants grow inside. The cave formed in limestone and is believed to be two to five million years old. Its name means 'cave of the mountain behind Đoòng'.

Discovery

A local man named Hồ Khanh found the entrance on 10 December 1990 while looking for agarwood, a valuable timber. The rushing water and strong wind scared him off, and he later forgot exactly where it was. He told British cavers about it, and in 2008 he found the entrance again. A British Cave Research Association team explored and surveyed the cave in 2009, and it reached the end of the passage in 2010 after climbing a 60-metre flowstone wall they called the Great Wall of Vietnam.

Inside the cave

The cave is so big that its cross-section is believed to be twice that of the next biggest passage, in Deer Cave in Malaysia. The roof has collapsed in two places, and light from these holes lets a jungle grow on the floor. The cave has some of the tallest known stalagmites in the world, up to about 80 metres. In 2019, explorers found that its river connects to a nearby cave called Hang Thung.

On the globe

The model shows a vast cave with sunlight pouring through collapsed roof holes onto a jungle inside.