The largest cave in the world is soon to be opened to tourists in Vietnam, tourism officials have disclosed.
The Son Doong Cave, discovered just 20 years ago, will be opened up on a test basis to visitors.
The tourism authority of Quang Binh Province said the cave would be open between February and August of next year, with small expeditionary groups of up to eight persons permitted entry.
"After that we will decide whether to keep the cave open on a regular basis," said the tourism authority's deputy director Nguyen Van Ky. "We'll be studying whether the visits will have any adverse environmental effects."
Tours must be booked via the Vietnamese tour operator Oxalis. Already, the company says it has more requests than it has capacity for in the coming year. Oxalis says a total of just 220 visitors to the cave are planned for 2014.
An expedition in Son Doong, located in the Phong Nha Ke Bang National Park 500 kilometres south of the capital Hanoi, is not for beginners.
Tourism officials say the underground trek is 17 kilometres. The expeditions will start after an overnight stay at the site. The cave contains spectacular rock formations and pools of water and unique flora and fauna, Nguyen says.
A tour costs 3,000 dollars per person. The national park was declared a World Natural Heritage site by UNESCO in 2003.
Local inhabitants of the area of central Vietnam bordering on Laos discovered the cave with its underground river in 1991.
In 2009, British scientists carried out the first expedition, with researcher Howard Limbert reporting a cavern length of 6,481 metres.
At some points it is 150 metres wide and 200 metres tall, surpassing what till then had been the largest known cave in the world, the Deer Cave on Borneo.