Five times larger than the nearby cave that previously held the record of the largest in Vietnam, Sơn Đoòng was named after the Vietnamese words for “mountain river,” because of its own large, fast-flowing river inside it.
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.
A group of cavers descends into Ellison's Cave far under Pigeon Mountain in northwest Georgia. The cave's "Fantastic Pit," seen here, is the deepest cave drop in the continental United States at a staggering 586 vertical feet.