Within one year, 243 tourists were taken safely into the cave on tours launched on a piloting basis.

Recognizing the tour’s success in drawing international tourists to Phong Nha – Ke Bang Park and contributing massive revenues to the province’s budget, the provincial People’s Committee decided to allow Oxalis, the tour provider, to launch more such tours.

The committee added that they will help develop the tours on a larger, professional scale.

The tours to Son Doong Cave, which last five days and four nights, offer adventure-seeking tourists opportunities to do trekking on an average of 10km a day and scale mountains at a height of at least 500m.

Tourists will also learn how to cross swift-flowing rivers and springs, climb rocky mountains with kits, explore grottos and master survival skills in extreme conditions.

New tours will be conducted from January to August in 2015, which means before and after the rainy, stormy season.

Son Doong Cave, which has a large fast-flowing underground river inside, was found by a local resident named Ho Khanh in 1991.

The cave became public after a group of British scientists from the British Cave Research Association, led by Howard and Deb Limbert, conducted a survey in Phong Nha-Ke Bang, a UNESCO World Heritage Site in April 2009.

According to the Limberts, Son Doong Cave is five times larger than the Phong Nha Cave, previously considered the biggest cave in Vietnam. The biggest chamber of Son Doong is more than five kilometers long, 200 meters high, and 150 meters wide.

With such large dimensions, Son Doong overtakes Deer Cave in Malaysia to grab the title of the world's largest cave.

Tuoi Tre News - September7, 2014