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.

Tsetse, six-year-old daughter of Dukha herder Erdenebat Chuluu, sits among her family's reindeer in a forest near the village of Tsagaannuur, Khovsgol aimag, Mongolia, April 21, 2018. Nyamaa is an ethnic Darkhad, herders of northern Mongolia who have historically inhabited the steppe that borders the Taiga forests. (Photo by Thomas Peter/Reuters)

South Korean youths play Pokemon Go on July 15, 2016 in Sokcho, South Korea. South Korea is not one of the initial Pokemon Go released countries, nor is the game likely to be released officially any time soon as the South Korean government does not allow Google to use its map; however, South Korean game enthusiasts are now visiting a handful of loophole areas in the north eastern side of the country near the border of North Korea to join the global frenzy of Pokemon Go. (Photo by Jean Chung/Getty Images)

A woman argues with police officer during a protest in support of jailed opposition leader Alexei Navalny in Ulan-Ude, the regional capital of Buryatia, a region near the Russia-Mongolia border, Russia, Wednesday, April 21, 2021. Navalny's team has called for nationwide protests on Wednesday following reports that the politician's health was deteriorating in prison, where he has been on hunger strike since March 31. Russian authorities have stressed that the demonstrations were not authorized and warned against participating in them. (Photo by Anna Ogorodnik/AP Photo)

A Turkana man and a boy carrying a gun look on as a G3 battle rifle hangs from a structure used to dry fish at a fishing camp on the shores of Lake Turkana, some kilometres from Todonyang near the Kenya-Ethiopia border in northwestern Kenya October 12, 2013The Turkana are traditionally nomadic pastoralists, but they have seen the pasture that they need to feed their herds suffer from recurring droughts and many have turned to fishing. However, Lake Turkana is overfished, and scarcity of food and pastureland is fuelling long-standing conflict with Ethiopian indigenous Dhaasanac, who have seen grazing grounds squeezed by large-scale government agricultural schemes in southern Ethiopia. The Dhaasanac now venture ever deeper into Kenyan territory in search of fish and grass, clashing with neighbours. Fighting between the communities has a long history, but the conflict has become ever more fatal as automatic weapons from other regional conflicts seep into the area. While the Turkana region is short of basics like grass and ground-water, it contains other resources including oil reserves and massive, newly discovered underground aquifers. (Photo by Siegfried Modola/Reuters)

In this March 7, 1991 file photo, a U.S. Marine patrol walks across the charred oil landscape near a burning well during perimeter security patrol near Kuwait City. Twenty five years after the first U.S. Marines swept across the border into Kuwait in the 1991 Gulf War, American forces find themselves battling the extremist Islamic State group, born out of al-Qaida, in the splintered territories of Iraq and Syria. The Arab allies that joined the 1991 coalition are fighting their own conflicts both at home and abroad, as Iran vies for greater regional power following a nuclear deal with world powers. (Photo by John Gaps III/AP Photo)

“Pripyat is a ghost town near the Chernobyl Nuclear Power Plant, within the Chernobyl Exclusion Zone, part of Kiev Oblast (province) of northern Ukraine, near the border with Belarus”. – Wikipedia

Photo: A view of empty houses in the deserted town of Pripyat near the closed Chernobyl nuclear power plant Ukraine, November 27, 2012. Pripyat, the city of 47,000 had already been evacuated after the April 26, 1986, explosion of Reactor No. 4 (Photo by Efrem Lukatsky/AP Photo)

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Lake Natron is a salt lake located in northern Tanzania, close to the Kenyan border, in the eastern branch of the East African Rift. The lake is fed by the Southern Ewaso Ng'iro River and also by mineral-rich hot springs. It is quite shallow, less than three meters (10 feet) deep, and varies in width depending on its water level, which changes due to high levels of evaporation, leaving concentrations of salt and other minerals, notably sodium carbonate (natron).