Sơn Đoòng Cave - The large moutain in the world.

Inside is a large, fast-flowing subterranean river. It was formed in Carboniferous/Permian limestone. 4]

Discovery
Sơn Đoòng Cave was discovered by a regional male named Hồ-Khanh in 1991. The whistling sound of wind and roar of a rushing stream in the cave heard through the entrance as well as the high descent avoided the local individuals from entering the cave. Only in 2009 did the cave ended up being globally understood after a group of researchers from the British Cave Research Association, conducted a study in Phong Nha-Kẻ Bàng from 10 to 14 April 2009.

Description
According to the Limberts, the cave is five times larger than nearby caves like Phong Nha Cave and Hang En, the third largest collapse the world formerly thought about the greatest cave in Vietnam. The greatest chamber of Sơn Đoòng is more than 5 kilometres (3.1 mi) long, 200 metres (660 feet) high and 150 metres (490 ft) broad. With these measurements, Sơn Đoòng surpassed Deer Collapse Malaysia in 2009 to take the title of the world's largest cave.The cave runs for approximately 9 kilometres (5.6 mi) and is punctuated by 2 big dolines, which are areas where the ceiling of the cave has actually broken down. The dolines permit sunlight to enter areas of the cave and has led to the development of trees as well as other plants.

The cave consists of some of the highest known stalagmites on the planet, which are up to 70 m high. Behind the Great Wall of Vietnam were discovered cave pearls the size of baseballs, an abnormally large size.

Traveler activities
In early August 2013, the first tourist group explored the cave on an assisted tour at an expense of US$ 3,000 each.Permits are needed to access the cave and are made available on a restricted basis. Just 500 authorizations were provided for the 2015 season, which runs from February to August. After August, heavy rains cause river levels to increase and make the cave largely inaccessible.

The whistling noise of wind and roar of a rushing stream in the cave heard through the entryway as well as the high descent avoided the regional people from entering the cave. Just in 2009 did the cave ended up being worldwide understood after a group of researchers from the British Cave Research Association, conducted a survey in Phong Nha-Kẻ Bàng from 10 to 14 April 2009. According to the Limberts, the cave is 5 times larger than close-by caves like Phong Nha Cave and Hang En, the third biggest cave in the world formerly considered the most significant cave in Vietnam. With these dimensions, Sơn Đoòng surpassed Deer Cave in Malaysia in 2009 to take the title of the world's biggest cave.The cave runs for roughly 9 kilometres (5.6 mi) and is stressed by 2 big dolines, which are locations where the ceiling of the cave has broken down. In early August 2013, the first tourist group checked out the cave on an assisted tour at an expense of US$ 3,000 each.Permits are needed to access the cave and are made readily available on a restricted basis.