It has room for a skyscraper with 40 floors and it contains both jungle and a river. The Son Doong cave in Vietnam is the largest in the world and a tour inside it is something quite out of the ordinary.
The enormous cave is situated in the Vietnamese national park Phon Nha-Ke Bang, 280 miles south of the capital Hanoi.
Sơn Đoòng Cave was found by a local man 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 steep descent prevented the local people from entering the cave. Only in 2009 did the cave become internationally known after a group of scientists from the British Cave Research Association, conducted a survey in Phong Nha-Kẻ Bàng from 10 to 14 April 2009. Their progress was stopped by a large, 60-metre (200 ft) high calcite wall, which was named the Great Wall of Vietnam. It was traversed in 2010 when the group reached the end of the cave passage.