What’s Hiding Beneath Vietnam Is Hard to Believe

Hidden deep in the jungles of central Vietnam lies Son Doong, the world's largest cave. It is so vast that it has its own weather system, with real clouds forming beneath a stone ceiling more than 650 feet high and an underground jungle growing on the cave floor. In 1990, a local man named Ho Khanh was sheltering from a storm in Phong Nha-Ke Bang National Park when he noticed wind and mist pouring out of a crack in a limestone cliff. He was too afraid to go inside. When he tried to return, he couldn't find the entrance again. It took him 18 years to rediscover it. In 2009, he led British cave explorers Howard and Deb Limbert to the entrance, and the world finally learned what had been hiding there. In this video, we explore how an underground river carved the largest cave passage on Earth out of ancient limestone. We look at how collapsed ceilings, called dolines, let sunlight in and allowed a jungle to grow underground, and why clouds appear inside the cave only in certain seasons. We also cover who controls access to Son Doong today and why a proposed cable car sparked global protest. Finally, we explain the surprising geological truth behind the cave's beauty: its jungles and clouds exist only because the cave is slowly falling apart. Would you join a multi-day expedition into Son Doong to see the clouds underground, or should places like this stay untouched? Tell us in the comments.