A mysterious lake has been discovered in Thung Cave within the World’s Natural Heritage Phong Nha-Ke Bang National Park, in the central province of Quang Binh.

Thanks to discoveries made during a recent expedition in Vietnam, it appears the world's largest cave, Son Doong, is even bigger than previously thought, CNN reports.

A new underground tunnel, which is far below the sea level, has been discovered in the world’s largest cave Son Doong in the central province of Quang Binh.