These new images, taken by Carsten Peter, capture the hidden depths of the worldâs biggest cave passage, in Vietnam’s Phong Nha-Ke Bang National Park.
The snapper spent two weeks at a time exploring the cavern, which was discovered by British explorers just two years ago.
Successive expeditions have yet to reach the end of the underground network, which has been found to house a forest.
âItâs a great feeling to photograph a newly discovered cave,â said Mr Peter from Munich, who took the shots when he joined British and German cavers on an expedition.
âI love to explore, I have been in some great caves in my lifetime and this is one of the most magnificent.
âTo see a cave so large it has a forest inside is superb â it was overwhelming. This is by far one of the most unique and unusual caves I have ever seen.â
An explorer is lowered into the Hang Son Doong (Pic: National Geographic/Caters/Carsten Peter)
At a mammoth 2.5 miles long, 100m (330ft) wide and 250m (800ft) high, Hang Son Doong, also known as Mountain River Cave, is as high as 25 double-decker buses.