A Viet Cong suspect holds his hands up after a Vietnamese Ranger from the 21st Vietnam Infantry Division routed him from his hiding place. (Photo by Keystone/Getty Images). 7th November 1967

Participants enjoy the “Color Me Run” festival in Hanoi, Vietnam, 28 May 2016. The festival which was inspired by the Holi Festival from India, attracted thousands of teenagers this year. (Photo by Luong Thai Linh/EPA)

Participants are covered by colored powder as they compete in The Color Run, a five-kilometre untimed race, in Hanoi, Vietnam September 26, 2015. Approximately 7,000 participants took part in Hanoi's first Color Run, reported local media. (Photo by Reuters/Kham)

“Tea Hills”. Early-morning mist over the tea hills of Phu Tho province in Vietnam. (Photo by Vu Trung Huan/Royal Meteorological Society’s Weather Photographer of the Year Awards)

A boat commutes across the Mekong river in Phnom Penh on August 8, 2014. The Mekong is the world's twelth longest river running from the Tibetan Plateau through China's Yunnan province, Myanmar, Laos, Thailand, Cambodia and Vietnam. (Photo by Tang Chhin Sothy/AFP Photo)

Vietnamese dentist Tran Phuong Thao and her husband Tran Minh Hieu wearing protective masks, kiss at their wedding ceremony during the coronavirus disease (COVID-19) outbreak in Hanoi, Vietnam on January 28, 2021. (Photo by Kham via Reuters)

Star Wars actors on the Cantina set at Star Wars Celebration: The Ultimate Fan Experience held at the Anaheim Convention Center on Thursday, April 16, 2015, in Anaheim, Calif. (Photo by Richard Shotwell/Invision/AP Photo)

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.