Hang Son Doong, which translates to Mountain River Cave, is the world’s largest single cave passage, based on its overall dimensions, according to the Guinness World Records. It is in the Phong Nha-Ke Bang National Park in Vietnam.
Just how big is it? The cave stretches more than 6.5 kilometres (about 4 miles) in length, towers roughly 655 feet high, and spans 490 feet across. With a total volume of at least 414.4 million cubic feet, it’s so immense that it has its own weather system.
Clouds form inside the cave from its underground river, and to put its scale into perspective, an entire city block of skyscrapers could fit comfortably within its massive chambers, according to Google Arts & Culture.
The cave was first stumbled upon in 1991 by a local man named Ho Khanh. Nearly two decades later, in April 2009, he guided a team of British cavers to the site, allowing them to begin exploring and mapping the interior as far as they could go.
Other spectacular features make Son Doong an amazing place: underground rivers, huge formations, dolines or skylights, ancient fossils, unique species of fish, insects, plants and trees.
Two large rivers, Khe Ry and Rao Thuong, join to form Son Doong Cave. The cave follows a large fault line that’s more than 300 feet wide, and it does see some sunlight, thanks to two skylights. Parts of the ceiling collapsed hundreds of thousands of years ago, resulting in dolines that let sunlight inside the cave.
The ethereal site has turned into a stunning destination for adventurers, but the only way to experience it is through Oxalis, a tour operator company that runs a five-night Son Doong Expedition Tour.
