Two men pull their boat over a railroad crossing in Nidderau-Eichen near Frankfurt, Germany, Friday, January 13, 2023. They came over the fields that were flooded by heavy rainfalls and continued their trip on the other side. (Photo by Michael Probst/AP Photo)

People dressed in Hanfu robes take a boat parade during the Xitang Hanfu Culture Week in the ancient town of Xitang on November 1, 2025 in Jiaixng, Zhejiang Province of China. (Photo by Wang Gang/China News Service/VCG via Getty Images)

Models showcase designs aboard fishing boats off Ngor Island during the 23rd Dakar Fashion Week, organized by Senegalese-French designer Adama N'Diaye, founder of the brand “Adama Paris”, on December 6, 2025, in Dakar, Senegal. (Photo by Cem Ozdel/Anadolu via Getty Images)

A man works on a small replica of the Iron Man armor next to a homemade replica of the “Hulkbuster” Iron Man armour from the movie “Avengers: Age of Ultron”, at an underground parking lot in Zhengzhou, Henan province, China, May 12, 2015. The 3.4-metre-tall replica is made of over 100 fiber-reinforced plastic components. It took Xing and his friends two months to put them together after watching the trailer of the movie in March, local media reported. (Photo by Reuters/Stringer)

The Al-Gaffal is an annual long-distance race between crews sailing 60-ft. traditional wooden boats called dhows and takes place in the Persian Gulf, between the island of Sir Bu Nair, near the Iranian coast and the Gulf emirate of Dubai. Photo: Traditional wooden boats, or dhows, compete at sunrise during the Al Gaffal race, a long-distance dhow sailing race, near Sir Bu Nuayr, near Sharjah May 18, 2014. (Photo by Martin Dokoupil/Reuters)

A Rohingya migrant who arrived in Indonesia by boat cries while speaking on a mobile phone with a relative in Malaysia, at a temporary shelter in Kuala Langsa in Indonesia's Aceh Province May 16, 2015. Nearly 800 migrants were brought ashore in Indonesia on Friday, but other vessels crammed with them were sent back to sea despite a United Nations call to rescue thousands adrift in Southeast Asian waters with dwindling food and water. Thousands of Rohingya Muslims fleeing Myanmar and Bangladesh are stranded on boats as regional governments block them from landing. (Photo by Roni Bintang/Reuters)

Farmers arrange bunches of water lilies after harvesting them from the wetlands in Barishal, Bangladesh on March 21, 2023. Floating through 10,000 acres of canal, farmers use their little boats to fetch the flowers. (Photo by Joy Saha/Cover Images)

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.