Hang Son Doong is the largest known cave in the world, with enough space in some of its passages for a Boeing 747 plane to pass through. The limestone cavern lies beneath lush jungle in Vietnam’s Phong Nha-Ke Bang National Park and is home to pristine forests that thrive on giant “skylights” in the rock.

Hang Son Doong Cave – whose name means “mountain river” – is young compared to other limestone caves. It was formed 2 to 3 million years ago within the largest limestone massif in Asia, a colossal block of rock more than 400 million years old, born from the compressed shells and skeletons of ancient marine animals. Two rivers – the Rao Thuong and the Khe Ry – flowed through cracks in the limestone and eroded the rock, forming a giant tunnel in the massif recently known as Son Doong.