Vietnam's Son Doong cave discovered by local man in 1990
The massive underground passage was confirmed as the world's largest single cave by British cavers in 2009.
A local man, Ho Khanh, discovered the entrance to Son Doong cave in central Vietnam in December 1990 while seeking shelter from heavy rain, according to the Times of India.
Khanh was searching for agarwood in the jungle when he noticed mist and cold air coming from a cliff opening.
After failing to find the entrance in 2007, Khanh returned to the jungle alone in 2008 and successfully marked the location.
A British-Vietnamese expedition led by caver Howard Limbert explored the site in 2009 and identified it as the largest known single cave passage.
Guinness World Records states the cave is at least 6.5 kilometres long, with a width of 150 metres and a height of about 200 metres.
The cave, located in Phong Nha-Ke Bang National Park, contains an underground river and vegetation that grows near collapsed ceiling sections.
Organised expeditions for visitors began in 2013.