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 Muslim Shi'ite boy carries a toy gun while standing next to a picture of Hezbollah leader Sayyed Hassan Nasrallah as he takes part in a march organised by Hezbollah during a re-enactment of the battle of Kerbala during a mourning process, ahead of the day of Ashura, in Saksakieh village, southern Lebanon, October 18, 2015. Ashoura, the most important day in the Shi'ite calendar, commemorates the death of Imam Hussein, grandson of the Prophet Mohammad, in the 7th century battle of Kerbala. (Photo by Ali Hashisho/Reuters)

A pedestrian battles against gale force winds in Adelaide Street West next to the promenade in Blackpool on December 28, 2011 in Blackpool, England. (Photo by Christopher Furlong/Getty Images)

(L-R) Natalie Burns and Taunia Arave battle as referee Nick Stevens (R) looks on during the US National Sumo Championships at the Riviera Hotel & Casino June 24, 2011 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)

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)

New York City FC midfielder Valentin Castellanos (11) falls after battling Columbus Crew defender Aboubacar Keita (30) for a high ball during the second half at Red Bull Arena in New York, August 24, 2020. (Photo by Vincent Carchietta/USA TODAY Sports)