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 four years ago.
A local man discovered the cave entrance in 1991, but British cavers were the first to explore it in 2009.
Amazing. Reminds me of all the Sci Fi movies and books about lost worlds here on and inside the earth.