The Son Doong Cave in Vietnam is the biggest cave in the world. It’s over 5.5 miles long, has a jungle and river, and could fit a 40-story skyscraper within its walls.
But nobody knew any of that until about six years ago.
The recently discovered cave has been touted as the largest in the world, although other caves vie for the title of longest (Mammoth Cave in Brownsville, Kentucky nabs that title with about 400 miles of passageways) and deepest (Krubera Cave in the nation of Georgia).
A local man discovered the cave entrance in 1991, but British cavers were the first to explore it in 2009. Tour company Oxalis has been running trial tours of the cave since two summers ago.