The worlds largest cave is located in Vietnam.
The Son Doong Cave in Vietnam is over 8.5 kilometers long, has a jungle and river, and could fit a 40-story skyscraper inside it.
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, as of 2009, believed to be twice that of the next largest passage.
It is the largest known cave passage in the world by volume.
Its name, Hang Sơn Đoòng, is variously translated from Vietnamese as 'cave of the mountain river' or 'mountain cave of Đoòng [village]'.
As a solutional cave, it was formed in soluble limestone and is believed to be between 2 and 5 million years old.