Hang Sơn Đoòng 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 cavers 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 flowstone-coated wall, which was named the Great Wall of Vietnam. It was traversed in 2010 when the group reached the end of the cave passage

Formed in Carboniferous/Permian limestone, the main Sơn Đoòng cave passage is the largest known cave passage in the world by volume – 38.4×106 cubic metres (1.36×109 cu ft), according to Howard Limbert. It is more than 5 kilometres (3.1 mi) 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 (5.6 mi) 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, resulting in the growth of trees as well as other vegetation.

By mid-2019, it became clear that the cave is connected by its underground river with a nearby cave called Hang Thung. This increases the effective volume of the cave by more than 1.6 million cubic metres.

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.

The scale of the site’s interior is so massive it could fit an entire New York block inside, including skyscrapers, or have a Boeing 747 comfortably fly through without its wings being in any danger.

In early August 2013, the first tourist group explored the cave on a guided tour at a cost of US$3,000 each. Permits are required to access the cave and are made available on a limited basis, with 1000 permits available for the 2019 and 2020 season, which runs from February to August. After August, heavy rains cause river levels to rise and make the cave largely inaccessible. As of 2017 only Oxalis Adventure Tours have permission to enter the cave for tourism purposes.