Son Doong Cave

Interesting facts

In places the passage is so vast that a Boeing 747 could fly through without its wings touching the walls.

Some sections are large enough to hold an entire New York city block, skyscrapers included.

The cave is so big that it makes its own weather: river mist and air from the collapsed dolines form fog and drifting clouds inside.

Trees up to about 30 metres tall grow in the cave's forest, and more than 200 plant species have been recorded underground.

The expedition named the first doline Watch Out for Dinosaurs, because its ferns, fog and sheer cliffs looked like a prehistoric scene.

The second doline shelters a jungle the explorers called the Garden of Edam, lit by sunlight falling from the collapsed roof.

From January to March, on sunny days around midday, shafts of sunlight pour through the first doline and cut through the mist.

One giant stalagmite is called the Hand of Dog, reportedly after a surveyor misheard Hand of God during the 2009 expedition.

Including all its passages, the cave runs for about 9 kilometres and reaches a maximum depth of around 150 metres.

The 2019 link to neighbouring Hang Thung added more than 1.6 million cubic metres to the system's potential volume.

Why it is worth it

Hang Sơn Đoòng, in the karst of Phong Nha–Kẻ Bàng National Park near the Laos border, holds the largest known cave passage on Earth. The main passage runs for more than 5 km, reaches about 200 metres in height and 150 metres in width, and its volume was measured at about 38.5 million cubic metres; its cross-section is thought to be roughly twice that of the next-largest passage, Deer Cave in Malaysian Borneo. The cave formed in limestone of Carboniferous–Permian age and is believed to be between two and five million years old. Its name means roughly "cave of the mountain behind Đoòng", after a nearby Vân Kiều village.

A local man, Hồ Khanh, found the entrance in 1990 while searching for agarwood, but was put off by the roar of water and the wind blowing out of it, and later could not find it again. He relocated it in 2008 at the request of British cavers, and in April 2009 an expedition of the British Cave Research Association led by Howard Limbert surveyed the cave. They were stopped by a flowstone barrier about 60 metres high, which they named the Great Wall of Vietnam, and crossed it in 2010 to reach the end of the passage. Two collapsed dolines let daylight into the cave, and under them grows a patch of forest; elsewhere there are stalagmites up to about 80 metres tall and cave pearls the size of baseballs. In 2019 divers found that its underground river connects with the neighbouring Hang Thung.

This is not a show cave with paths and lights. Access is by permit and in small numbers: the first commercial expedition went in 2013, and since 2017 only one licensed operator, Oxalis Adventure, has been allowed to take visitors. Trips are demanding multi-day camping expeditions graded as challenging, and they call for real fitness. The cave is closed to tourism from September to December, when monsoon rains raise the river to dangerous levels and the ecosystem is left to recover. A proposed cable car through the cave was abandoned after opposition from conservationists and residents. The wider national park, a UNESCO World Heritage Site since 2003, has some 300 caves and grottoes; Phong Nha Cave, which gave the park its name, is the classic way to see the karst without an expedition.

Getting there

The cave lies in remote forest about 30 km from the town of Hoàn Lão; expeditions start from the Phong Nha area, where the park's tourist services are based. Dong Hoi Airport (VDH), with domestic flights from Hanoi and other cities, is about 33 km away in a straight line. Entry is possible only on an organised expedition with the licensed operator; book well in advance and check season dates before planning.

Son Doong Cave

Interesting facts

Why it is worth it

Getting there

Plan your visit

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