Son Doong Cave
(Quảng Trị, Vietnam)

Located in Phong Nha-Kẻ Bàng National Park in Vietnam, Son Doong is the largest known cave in the world by volume — so vast that it contains its own weather system, its own river, and sections where the ceiling has collapsed to create isolated jungle ecosystems lit by shafts of natural light.

Clouds form inside it and a Boeing 747 could fly through its largest chamber. It was only discovered by a local farmer in 1990 and not fully explored by scientists until 2009, even today only a small number of visitors are permitted inside each year!