Hang Son Doong skyhole by John Spies. The Son Doong Cave in Vietnam is the biggest cave in the world. It's over miles long, has a jungle and river, and could fit a 40 story skyscraper within its walls. It was discovered by modern man 5 years ago.
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.