Explore the ancient caves of Hang Son Doong, Vietnam. Hang Son Doong is one of the largest caves in the world and features a fast-flowing underground river. For spelunkers, exploring Hang Son Doong is the equivalent of scaling Mount Everest.
At more than high, wide and long, the Hang Son Doong cave in Vietnam is so big it has its own river, jungle and climate. Australian photographer John Spies, spent a week photographing the natural wonder