The Vietnam Book of Records (VietKings) is filing application for the World Records Union (WorldKings) to recognise Son Doong Cave as the largest natural cave in the world.
Son Doong Cave. Photo by Ryan Deboodt.
Son Doong Cave, located in Phong Nha-Ke Bang National Park in the central province of Quang Binh, is large enough to fit a 40-storey skyscraper inside. It is more than 200m high, 150m wide and approximately 5 to 6.5km long.
Son Doong Cave was formed between 2 and 5 million years ago with its all ecosystem including a jungle and a river.
The cave was first classified as the largest in the world by the British Cave Research Association in 2009. It was also listed among the "52 Places to Go in 2014" by The New York Times.
Last year, a tour of five days and four nights to Son Doong cost 500 lucky tourists a good $3,000 each. The high price is justified by conservation efforts in the cave system and guaranteeing safety for tourists. Only travel firm Oxalis has the right to run tours to the cave.
Tourists choosing to take the tour are also advised to prepare vigorously for the tour.
All Son Doong tours offered by the company for 2016 are fully booked.