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)

Dina Asher-Smith of Great Britain reacts after competing in the women's 200m during the Wanda Diamond League Golden Gala meeting. Dina Asher-Smith placed first. (Photo by Ciro De Luca/Reuters)

Vietnam's Khuat Phuong Anh (R) celebrates winning the women's 800m final during the 31st Southeast Asian Games (SEA Games) at My Dinh National Stadium in Hanoi on May 16, 2022. (Photo by Navesh Chitrakar/Reuters)

Runner-up; Hon Yen marine ecosystem. Phu Yen, Vietnam. Every year between May and August, the coral of this rich and diverse ecosystem becomes exposed at low tide. (Photo by Truong Hoai Vu/Royal Society of Biology Photography Competition)

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.

Damaged vehicles sit on Yeongjong Bridge in Incheon, South Korea, Wednesday, February 11, 2015. Two people were killed and at least 42 were injured on Wednesday after a pileup involving about 100 vehicles in foggy weather on the bridge near the Incheon International Airport, South Korean officials said. (Photo by Suh Myung-gon/AP Photo/Yonhap)

Visitors enjoy a walk accross a suspension bridge for the pedestrians that is the longest such construction in the world shortly after its official opening at a mountain resort in Dolni Morava, Czech Republic, Friday, May 13, 2022. The 721-meter (2,365 feet) long bridge is built at the altitude of more than 1,100 meters above the sea level. It connects two ridges of the mountains up to 95 meters above a valley between them. (Photo by David W. Cerny/Reuters)

Cars slowly move along a bridge in traffic jam in central Moscow, Russia on December 11, 2018. (Photo by Yuri Kadobnov/AFP Photo)