Paramedics wearing protective suits amid fears of coronavirus outbreak check on a man who collapsed outside a clinic in Jakarta, Indonesia, Thursday, March 26, 2020. It's not immediately clear what caused the man to collapse. The U.S. Embassy in Indonesia has ordered the departure of employees' family members under the age of 21 from its missions in the country where new COVID-19 patients have surged in the past week with high fatality. (Photo by Muchlis Akbar/AP Photo)

A man protesting the Ferguson grand jury decision to not indict officer Darren Wilson in the Michael Brown case is arrested while marching through the streets on December 1, 2014 in New York City. Brown, an 18-year-old black man, was killed by Darren Wilson, a white Ferguson, MO police officer, on August 9. (Photo by Andrew Burton/Getty Images)

A man invades the Red Carpet and is held by security at the “How To Train Your Dragon 2” Premiere at the 67th Annual Cannes Film Festival on May 16, 2014 in Cannes, France. The man stuck his head up America`s skirt before being dragged away by security. Pictured: Djimon Hounsou, Cate Blanchett, America Ferrera and Kit Harington. (Photo by Camilla Morandi/IPA)

Police officers react as they attempt to detain a protestor near the entrance to Downing Street, during an anti-racism demonstration in London, on June 3, 2020, after George Floyd, an unarmed black man died after a police officer knelt on his neck during an arrest in Minneapolis, USA. Londoners defied coronavirus restrictions and rallied on Wednesday in solidarity with protests raging across the United States over the death of George Floyd, an unarmed black man who died during an arrest on May 25. (Photo by Daniel Leal-Olivas/AFP Photo)

A young man “painting” the Eiffel Tower. (Photo by Keystone/Getty Images). 9th May 1970

A member of the pro-government “red shirt” movement attacks a Buddhist monk outside the National Anti-Corruption Commission office in Nonthaburi province, on the outskirts of Bangkok March 24, 2014. Members of the movement attacked the monk after he shouted complaints to the group blocking a road near the National Anti-Corruption Commission. (Photo by Chaiwat Subprasom/Reuters)

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.