Inside Son Doong: The Expedition Through the World’s Largest Cave
A cave passage five kilometres long and 200 metres high, with two jungles growing inside it, was surveyed only in 2009. A limited number of visitors may cross it each year on a guided expedition.
Hang Son Doong lies in Phong Nha-Ke Bang National Park, in the limestone mountains of central Vietnam near the border with Laos. It is the largest cave passage known on earth. It has been open to visitors since 2013, in small numbers and on one condition: they must walk and camp their way through it.
How it was found
In December 1990 a local man, Ho Khanh, was in the forest looking for agarwood when he came upon an opening in a cliff from which wind and the sound of a river were issuing. He did not go in, and afterwards could not find the place again. British cavers who had been exploring the region for years asked him to keep looking. He found it again in 2008, and in April 2009 a team from the British Cave Research Association surveyed it.
The scale
The main passage is more than five kilometres long. In places it is 200 metres high and 150 metres wide, large enough to hold a city block of forty-storey towers. Its volume is put at 38.5 million cubic metres, about twice that of the next largest, Deer Cave in Sarawak.
In two places the roof collapsed long ago and left openings to the sky. Light and rain enter through these dolines, and forest has grown up on the rubble beneath them, with trees thirty metres tall, 200 metres below the surface. Cloud forms inside the cave and drifts along the passage. There are stalagmites up to 80 metres high and beds of cave pearls the size of oranges. Near the far end a wall of flowstone 60 metres high, which the first explorers called the Great Wall of Vietnam, blocked the way until it was climbed.
The expedition
One company, Oxalis Adventure, holds the licence to take visitors through. The expedition lasts six days and five nights in all. The group walks through jungle and across rivers, explores Hang En, itself one of the largest caves in the world, and camps in the forest near the entrance to Son Doong. The next two nights are spent inside the cave, beside each of the two dolines. Each group of ten is accompanied by a caving expert, a guide, safety assistants, cooks and porters, about thirty people in all. The exit is a climb of ninety metres up the Great Wall by ropes and ladders.
The season runs from January to August, and the cave is closed for the rest of the year. The price is about 3,000 US dollars a person. Departures are sold out about two years ahead.
Who can do it
No caving experience is required, but the trip is demanding. It involves some 28 kilometres of jungle trekking and nine of caving, with about fifty river crossings, scrambling over boulders and climbing on fixed ropes. The operator asks for evidence of a recent overnight trek and good fitness, and accepts guests aged 18 to 70.
For travellers
The base is the village of Phong Nha, reached from Dong Hoi, which has flights from Hanoi and Ho Chi Minh City and a station on the main north-south railway. Those without the time or the fitness can visit Paradise Cave and Phong Nha Cave in a day, or take a shorter expedition to Hang En. The park pairs well with the old capital of Hue, three hours to the south, and with a journey down the coast on The Vietage.