In the heart of Vietnam’s Phong Nha-Ke Bang National Park is Hang Son Doong (Mountain River Cave). It is the largest known cave passage in the world. At three miles long and 656 feet high in some places, it’s home to a river, jungles, the largest stalagmite ever found (262 feet) and a microclimate all its own. Hang Son Doong is so big it could accommodate an entire city block of 40-story skyscrapers. Incredibly, it was only discovered 27 years ago by a local logger seeking shelter from a storm. It is now in a UNESCO-listed park.
Photo credit: Lelong (Kênh14)