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.

Long-tailed mayflies (Palingenia longicauda) at Tisza river near Tiszainoka 135km (84 miles) southeast of Budapest, June 23, 2013. Millions of these short-lived mayflies engage in a frantic rush to mate and reproduce before they perish in just a few hours during “Tiszaviragzas” or Tisza blooming season from late spring to early summer every year. (Photo by Laszlo Balogh/Reuters)

Two holy men with a decorative faces and headdresses, taken in Kathmandu, Nepal. Wandering through the cities and forests of Nepal are the holy men, or Sadhus, who have left all materialistic pleasures behind to live a life devoted to God. Their appearances vary from brightly coloured face paints, and decorations, to minimalistic practical clothing, but they all represent the fundamental values and meanings of Hinduism. Danish photographer Jan Moeller Hansen visited the ancient capital city of Kathmandu between 2013 and 2016 and documented the mysterious holy wanderers. (Photo by Jan Moeller Hansen/Barcroft Images)

Typhoon Yolanda – also known as Haiyan – struck the central part of the country November 8, 2013, leaving at least 6,300 people dead and over four million displaced. A month after Typhoon Haiyan, the United Nations Population Fund estimates that 5,000 women were subjected to sеxual violence. A study by the Health and Human Rights online publication shows the majority of young girls and women in Manila’s sеx industry come from poverty-stricken areas – such as Leyte, Samar, Cebu and southern Mindanao – and enter trafficking through force, deception, economic desperation and psychological manipulation. (Photo by Hannah Reyes Morales/The Washington Post)

A student falls asleep as she holds a book containing a portrait of China's late chairman Mao Zedong during a lesson at the Democracy Elementary and Middle School in Sitong town, Henan province December 3, 2013. In a remote part of central China, the day starts at the Democracy Elementary and Middle School with a pre-dawn jog, some revolutionary songs and then an activity long since forgotten at other schools: reciting quotations from Mao Zedong's famed “Little Red Book”. While the ruling Communist Party that Mao led continues to hold him in esteem as the leader of the Communist Revolution, his radical policies and teachings have been largely shelved since his death in 1976 in favour of a pro-market approach that has turned China from a backwater into the world's second biggest economy. The 120th anniversary of Mao's birth is on December 26, 2013. (Photo by Carlos Barria/Reuters)

A woman reacts as she joins around a thousand New Year swimmers, many in costume, braved freezing conditions in the River Forth in front of the Forth Rail Bridge during the annual Loony Dook Swim on January 1, 2013 in South Queensferry, Scotland. Thousands of people gathered last night to see in the New Year at Hogmanay celebrations in towns and cities across Scotland. (Photo by Jeff J. Mitchell)

Revelers participate in the traditional Bloco da Lama (Mud block) carnival in Parati, Rio de Janeiro State, Brazil, on February 9, 2013. The event, which was begun by two men in a playful manner in 1986, has now become a traditional carnival in which participants disguised as primitives with rags, lianas or skulls and bones, dive in the mud. (Photo by Victor Moriyama/AFP Photo)

A newly-married couple takes a nap before their mass wedding ceremony at the CheongShim Peace World Center in Gapyeong, South Korea, Sunday, February 17, 2013. Some 3,500 South Korean and foreign couples exchanged or reaffirmed marriage vows in the Unification Church's mass wedding arranged by Hak Ja Han Moon, a wife of the late Rev. Sun Myung Moon, the controversial founder of the Unification Church. (Photo by Lee Jin-man/AP Photo)