The 500-permit limit for entrance to Son Doong Cave this year has been fully booked, said Nguyen Chau A, General Director of Oxalis Adventure Tours.

Tourists from the US booked the majority of permits with 145 people, followed by Australians and Vietnamese with 123 and 115 adventurers, respectively.

Son Doong, located in the central province of Quang Binh, was first discovered by a local man in 1991 and made public by the United Kingdom’s Royal Geographical Society in 2009 and is considered the world’s biggest cave.

The cave is about 200 metres wide and over 150 metres high. With its largest chamber estimated at 250 metres tall, the cave is said to have enough space to accommodate a 40-storey skyscraper.

It contains at least 150 individual grottos, a dense subterranean jungle, and several underground rivers.

It has made headlines in prestigious magazines and on television channels, including the National Geographic in 2011 and recently on the American Broadcasting Company channel.

Recently, Boredpanda website – a leading art, design and photography community – listed Vietnam’s Son Doong Cave among top 15 unbelievable places that could belong to another planet.

The local government has permitted Oxalis Adventure Tours to organise tours of the cave at 3,000 USD per adventurer and with a strict limit of 500 tourists annually.

Up to 250 adventurers have explored the Cave so far this year.

VNA