A Vietnamese resort company has been granted approval to begin surveys to build a 10.6 kilometer (6.6 mi) long cable car in the world’s largest cave, the UNESCO-listed Son Doong in north-central Quang Binh province in Vietnam. If completed it would make it the longest cable car ride in the world, ahead of Tianmen Shan in China.

Vietnam has a fondness for cable cars. They pop up in many tourist spots, from the Ba Na hills in the center of the country to provincial spots popular with domestic tourists such as Nui Ba Den (Black Lady Mountain), south of Saigon. However, the prospect of this cable car, to be built by the large Sun Group (which owns the InterContinental Hotel in Danang and built the Ba Na hills cable car system), has upset environmentalists, the cave’s original discoverers and inspired an online petition.

The proposed $212 million cable car system would travel through Tien Son and Phong Nha caves (the latter was formerly believed to be the largest cave in Vietnam) and then Son Doong cave, with three of its seven stations in the 9 kilometer long Son Doong.

Son Doong was discovered by local Ho Khanh in 1991 and explored by a group from the British Cave Research Association in 2009, led by Howard and Deb Limbert. The UNESCO-listed cave receives under 250 visitors a year who all trek with the one travel company licensed to offer tours, Oxacis Tours. Those doing so have to trek and camp, with porters carrying baggage and food.

Whilst Son Doong still hosts few visitors the other caves, such as Phong Nha, within the Phong Nha-Ke Bang national park are far more touristed. The area has received 2.5 million visitors this year so far and this may rise to three million in 2015, according to Vietnamese news sources. The impacts of mass tourism are already being felt and experts worry that extending that to the pristine Son Doong, which is so large it contains a jungle and could fit skyscrapers within it, would be reckless at best.

Dang Minh Truong, Sun’s CEO, told Saigon-based Tuoi Tre News that the project will involve foreign experts and satisfy UNESCO’s criteria for sustainable development. He also noted that 80 UNESCO-listed sites already have cable car systems (though it should be noted that none of those are in remote cave systems within national parks).

Howard Limbert, who first explored the cave in 2009, has explored hundreds of caves in the area, is one of those staunchly against the idea of a cable car system. "The damage to Son Doong cave would be irreversible, and the cable cars would rob the cave of its pristine charms and the adventure thrills it has to offer," he told Tuoi Tre News. "The construction would also take its toll on the cave’s surrounding areas."

An online petition has been organized against the venture. It states, "This project is suicidal and have an infinite damaging impact on the Son Doong Cave and the ecosystem of the entire region at Phong Nha - Ke Bang National Park."