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.

In this March 15, 2012 file photo, a Chinese woman poses for photos near a sculpture depicting a Chinese yuan note at an art district in Beijing, China. China devalued its tightly controlled currency on Tuesday, August 11,2015, following a slump in trade, triggering the yuan's biggest one-day decline in a decade. The central bank said the yuan's 1.3 percent fall was due to a change aimed at making its exchange rate controls more market-oriented. But any change raises the risk of tensions with China's trading partners. (Photo by Ng Han Guan/AP Photo)

Syrians gather during an evacuation operation of rebel fighters and their families from rebel-held neighbourhoods on December 15, 2016 in the embattled city of Aleppo. A convoy of ambulances and buses left rebel territory in Aleppo in the first evacuations under a deal for opposition fighters to leave the city after years of fighting. The rebel withdrawal will pave the way for President Bashar al-Assad's forces to reclaim complete control of Syria's second city, handing the regime its biggest victory in more than five years of civil war. (Photo by Karam Al-Masri/AFP Photo)

A child blowing confetti from her hands during a Carnival parade in Cyprus' coastal city of Limassol, Sunday, March 13, 2016. Limassol's long-established parade is Cyprus' biggest and most famous, drawing revelers from across the east Mediterranean island. This year's parade drew huge crowds as people sought lighthearted reprieve from the bailed-out country's recession. The parade marks the start of the 40-day fasting period of Lent in the run-up to the Orthodox Christian Easter. (Photo by Petros Karadjias/AP Photo)

A visitor tries out Lenovo augmented reality glasses with the Star Wars Jedi Challenges during the Mobile World Congress in Barcelona, Spain, February 26, 2018. The Mobile World Congress, the world' s biggest mobile fair, is held in Barcelona from February 26 to March 1. (Photo by Yves Herman/Reuters)

Revellers cool themselves in the Danube River during the Sziget music festival on an island in Budapest, Hungary August 12, 2015. The event is one of the biggest cultural events of Europe, offering art exhibitions, theatrical and circus performances and music concerts. Almost 200 performers from 47 countries will entertain the hundreds of thousands of visitors from 11 to 18 August. (Photo by Laszlo Balogh/Reuters)

A girl plays with colourful papers at the 23rd Sziget (Island) Festival on Shipyard Island in Budapest, Hungary, 13 August 2015. The festival is one of the biggest cultural events of Europe, offering art exhibitions, theatrical and circus performances and music concerts. Almost 200 performers from 47 countries will entertain the hundreds of thousands of visitors from 11 to 18 August. (Photo by Balazs Mohai/EPA)

An Acehnese female police officer wear a hijab on duty in the street in Banda Aceh, Indonesia, 27 March 2015. Indonesia National Police officially issued a regulation allowing female police officer to wear the Islamic hijab (heads craft) as a part of their uniform. Indonesia is the biggest Muslim population in the world. (Photo by Hotli Simanjuntak/EPA)