Hang Son Doong ('cave of the mountain river' in Vietnamense) is a 9 km cave located near the Laos–Vietnam border. It has in the world.
Inside is a large, fast-flowing .
The cave a group of British explorers conducted a survey in April 2009.
They discovered a 60-metre high calcite wall, .
The cave also stalagmites in the world, which are up to 70 m tall.
The sunlight enters sections of the cave and trees and other vegetation.