Son doong cave is a cave in Phong Nha-Kẻ Bàng National Park, Bố Trạch district, Quảng Bình Province, Vietnam. Currently the biggest known cave in the world, the cave is located near the Laos-Vietnam border. Inside is a large, fast-flowing underground river.
In early August 2013, the first tourist group explored the cave on a guided tour at a cost of US$3,000 each. The group had six members from Australia, Norway, Russia and USA and spent 7 days and 6 nights for the tour. Next exploration trips will be arranged.

A three wheeled “cabin” scooter manufactured by German aircraft engineers Messerschmitt & Co at factories in Regensburg. (Photo by Hans Enzwieser/BIPs/Getty Images). 1955

Merit Prize Winner: “A Well Earned Rest in the Sahara”. This photo of Moussa Macher, our Tuareg guide, was taken at the summit of Tin-Merzouga, the largest dune (or erg) in the Tadrat region of the Sahara desert in southern Algeria. Moussa rested while waiting for us to finish our 45-minute struggle to the top. It only took ten minutes of rolling, running, and jumping to get back down. The Tadrat is part of the Tassili N'Ajjer National Park World Heritage area, famous for its red sand and engravings and rock paintings of cattle, elephants, giraffes, and rhinos that lived there when the climate was milder. Photo location: Summit of Tin-Merzouga, Tadrat, Tassili N'Ajjer National Park, Algeria. (Photo and caption by Evan Cole/National Geographic Photo Contest)

Jaison Vargas, crocodile tour guide, takes a picture of an American crocodile (Crocodylus acutus) during a tour at the Tarcoles river, in Tarcoles, Garabito municipality, Costa Rica, on March 31, 2022. Crocodile tours in the estuary of the Tarcoles River are a popular attraction for visitors to Costa Rica's Pacific coast, as the area gets back on its feet after being shaken by the pandemic. The river is home to nearly 500 species of birds and some 2,000 American crocodiles, many of which have been named after famous people. (Photo by Luis Acosta/AFP Photo)

An adult female Masai giraffe rears on its hind legs as it resists efforts by Kenya Wildlife Services (KWS) rangers to guide it into a transportation crate using ropes during an exercise to translocate large herbivores from Kedong Ranch due to land subdivisions and corralling that have disrupted wildlife migratory routes in Naivasha, Nakuru County, on November 16, 2025. Driven by two long ropes held by about twenty rangers, the blindfolded giraffe enters a tall trailer that is to transport it out of its natural habitat in the Rift Valley, which is deteriorating after having been resold. This is the first step in a meticulous relocation operation in the vast Kedong ranch, part of an ancestral corridor between Mount Longonot and Hell's Gate Park, near the iconic Lake Naivasha. (Photo by Tony Karumba/AFP Photo)

An engineer (L) talks to a driver of a dump truck loaded with gold-bearing soil at the Vostochny opencast of the Olimpiada gold operation, owned by Polyus Gold International company, in Krasnoyarsk region, Eastern Siberia, Russia, June 30, 2015. Polyus Gold International is the largest gold producer in Russia and one of the top 10 gold miners globally by ounces produced, according to the official web site of the company. Olimpiada is Polyus Gold's largest operation. (Photo by Ilya Naymushin/Reuters)

Amy Rimmer, Research Engineer at Jaguar Land Rover, demonstrates the car manufacturer's Advanced Highway Assist in a Range Rover, which drives the vehicle, overtakes and can detect vehicles in the blind spot, during the first demonstrations of the UK Autodrive Project at HORIBA MIRA Proving Ground in Nuneaton, Warwickshire on Friday October 21, 2016. (Photo by Fabio De Paola/PA Wire)

Visitors take pictures inside Kuala Lumpur Tower's “Sky Box”, one of the city's touristic attractions, in Kuala Lumpur, Malaysia, 05 January 2024. Malaysian Tourism Minister Tiong King Sing recently said that the tourism industry “is not just an engine for economic growth but also a bridge for cultural exchange and international friendship”. (Photo by Fazry Ismail/EPA/EFE)