Son Doong Cave

The world's biggest cave — with a forest and river inside

Son Doong is the biggest cave in the world: a 40-storey building would fit inside, and a plane could fly through! A river runs through it, and where the roof has collapsed, light pours in and a forest has grown — with 30-metre trees! The cave has its own clouds and mist. A local farmer found it in 1991, but no one went inside until 2009. Only 1,000 people a year are allowed in.

Son Doong (Hang Sơn Đoòng — 'mountain river cave') is in Phong Nha-Ke Bang National Park (UNESCO), central Vietnam; British cavers (Howard Limbert) surveyed it in 2009: 9 km long, with a main passage 200 m high and 150 m wide and a volume of 38.5 million m³ — the largest cave passage in the world. It was carved 2–5 million years ago by the Rao Thuong river dissolving limestone. Two giant dolines (roof collapses) — the 'Garden of Edam' and 'Watch Out for Dinosaurs' — hold a rainforest with 30 m trees, monkeys and flying foxes. The 'Great Wall of Vietnam', a 90 m calcite wall, was climbed in 2010. Its 80 m stalagmites are the tallest known. It has its own microclimate, with clouds under the roof. In 2019 divers found an underwater tunnel to the neighbouring Hang Thung cave, adding 1.6 million m³. Expeditions take 4 days; 1,000 visitors a year.

Fun facts

• A 40-storey building would fit inside Son Doong, which has its own clouds.
• The farmer who found the cave in 1991 forgot where it was for 18 years.
• A forest with 30-metre trees and monkeys grows inside the cave.