Son Doong in Vietnam is the largest cave in the world by volume. Some of its chambers are 200 metres tall and 150 metres wide - big enough to comfortably hold a 40-storey skyscraper or a Boeing 747.
The cave is so massive that it has its own weather. When warm humid air drifts in from outside it cools and forms actual clouds floating inside the chamber. Two collapsed sections of the ceiling let sunlight in, where a complete jungle has grown, river-cut and birds-included.
A local farmer accidentally found the cave in 1991 when he sheltered from a storm. He couldn’t get back to the entrance for years - only in 2009 did a British cave-exploring team finally survey the inside. Even today only a few hundred tourists are allowed in each year.
