The colourful process of salt harvesting is captured at the Hon Khoi Salt Fields in Nha Trang, Vietnam in December 2022. (Photo by Hilton Chen/Solent News & Photo Agency)

Nguyen Ngoc Anh, 36, who was an illegal logger turned forest protector poses at Phong Nha National Park, Quang Binh province, Vietnam on April 8, 2022. (Photo by Hoang Trung/Reuters)

A woman works at a factory producing clay pots at Phu Lang pottery village in Bac Ninh province, Vietnam, May 14, 2015. The village is part of an old pottery triangle in northern Vietnam which includes Bat Trang and Tho Ha, and has been producing pottery since the 13th century, according to local media. (Photo by Reuters/Kham)

This photograph taken on June 8, 2021 shows a street vendor walking past narrow residential houses, known as “nha ong” in Vietnamese or “tube houses”, in an urban area of Hanoi. (Photo by Manan Vatsyayana/AFP Photo)

Vietnamese artist Hoang Tien Quyet produces curved paper forms using a difficult technique known as wet-folding. This adds an element of sculpture to the work, making Hoàng’s origami animals truly remarkable. Too little water and the paper dries before the folding is done; too much water, and the paper will rip.

Promotional models use their smartphones during their break at the Global Mobile Internet Conference in Beijing May 6, 2014. Mobile Internet industry executives, developers and investors from more than 30 countries took part in the Global Mobile Internet Conference in Beijing, the organiser said. (Photo by Kim Kyung-Hoon/Reuters)

This picture taken on May 24, 2019 shows Mariam the dugong as she is cared for by park officials and veterinarians from the Phuket Marine Biological Centre on Libong island, Trang province in southern Thailand. An orphaned baby dugong rescued off a beach in Krabi province is Thailand's newest star, capturing the hearts of millions on social media and igniting an awarness for ocean conservation as authorities hand-raise the young mammal. (Photo by Sirachai Sirachai Arunrugstichai/AFP 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.