[1] Located near the Laos–Vietnam border, Hang Sơn Đoòng has an internal, fast-flowing subterranean river and the largest cross-section of any cave, worldwide,[2][3] believed to be twice that of the next-largest passage.

[7] The entrance to Hang Sơn Đoòng was found in 1991 by a local man named Hồ Khanh, while searching for agarwood, a valuable timber.

Although he initially went to investigate further, he was discouraged upon approach by the sound of rushing water and the strong wind issuing from the entrance.

[8] Later, he mentioned his discovery in passing to two members of the British Cave Research Association (BCRA), who were exploring in the local area.

[10] The expedition returned in March 2010 and successfully traversed the wall, which allowed the explorers to reach the end of the cave passage.

[17] The cave's interior is so large that it could fit an entire New York block inside, including skyscrapers, or could have a Boeing 747 fly through it without its wings touching either side.