Surrounded by jungle and used in the Vietnam war as a hideout from American bombardments, it is so large that it could hold a block of 40-storey skyscrapers. Its entrance was only rediscovered last year.
The photograph was taken by a British expedition returning to the rugged Phong Nha-Ke Bang National Park near the border with Laos.
The cave, lit from above through a skylight, is one of a network of some 150 connected caverns, many still not surveyed, in the Annamite mountains.
Story Link and Slideshow via Super Punch | Photo: National Geographic/Carsten Peter