SON ĐOONG CAVE, VEITNAM
Time for Travel: February to August
How To Reach: Arrive to Da Nang Airport, Veitnam. Travel 6 Hours to Phong Nha-Kẻ Bàng National Park.
Sơn Đoòng Cave, is a solutional cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch District, Quảng Bình Province, Vietnam. It has the WORLD LARGEST KNOWN CAVE PASSAGE CROSS-SECTION, and is located near the Laos–Vietnam border. It is more than 5 kilometres (3.1 mi) long, 200 metres (660 ft) high and 150 metres (490 ft) wide. Inside is a large, fast-flowing subterranean river. It was formed in Carboniferous/Permian limestone and is believed to be between 2 and 5 million years old.
Permits are required to access the cave and are made available on a limited basis