So Doing Cave,Quang Binh Provide,Vietnam. ![image](https://i.imgur.com/wbN02TS.jpg)

Sơn Đoòng Cave : (Vietnamese: Hang Sơn Đoòng )Known As cave of the mountain river or 'mountain cave of Đoòng village in Vietnamese, cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch District, Quảng Bình Province, Vietnam. As of 2009 it has the largest known cave passage cross-section in the worldand is located near the Laos–Vietnam border. Inside is a large, fast-flowing subterranean river. It was formed in Carboniferous/Permian limestone. It was created 2-5 million years ago by river water eroding away the limestone underneath the mountain Where the limestone was weak, the ceiling collapsed creating huge skylights. According to the Limberts, the main Sơn Đoòng cave passage is the largest known cave passage in the world by volume. It is more than 5 kilometres long, 200 metres (660 ft) high and 150 metres (490 ft) wide. Its cross-section is believed to be twice that of the next largest passage, in Deer Cave, Malaysia. The cave runs for approximately 9 kilometres and is punctuated by 2 large dolines, which are areas where the ceiling of the cave has collapsed. The dolines allow sunlight to enter sections of the cave which has resulted in the growth of trees as well as other vegetation. The cave contains some of the tallest known stalagmites in the world, which are up to 70 m tall. Behind the Great Wall of Vietnam were found cave pearls the size of baseballs, an abnormally large size. Son Doong cave was classified as the largest cave in the world by BCRA (British Cave Research Association) and selected as one of the most beautiful in the globe by the BBC news. . MoreInformation: Source:http://www.sondoongcave.org/son-doong-cave