A mother and her daughter paddle during a Stand Up Paddle (SUP) race of the Alpine Lakes Tour, on Europe's biggest underground lake, in St-Leonard, Switzerland, March 10, 2018. SUP is an offshoot of surfing that originated in Hawaii. Unlike traditional surfing where the rider sits until a wave comes, stand up paddle boarders stand on their boards and use a paddle to propel themselves through the water. (Photo by Denis Balibouse/Reuters)

Hannah Rice, 18, jumps from a stump after posing for a photograph next to a large bust of President Franklin D. Roosevelt while touring busts of U.S. presidents in Williamsburg, Va. on March 30, 2019. The statues were once part of an attraction called Presidents Park, which has since closed. (Photo by Matt McClain/The Washington Post)

Tour guides wearing traditional Chinese dress practice smiling by biting chopsticks at Qingming Grand-River Park in Kaifeng, central China's Henan Province on March 2, 2017, aiming to provide better service for visitors. (Photo by IPA Asia via ZUMA Wire)

A supporter dressed as flamingo cheers on the riders during the 12th stage of the 102nd Giro d'Italia – Tour of Italy – cycle race, 158kms from Cuneo to Pinerolo on May 23, 2019. (Photo by Marco Bertorello/AFP Photo)

U.S. first lady Melania Trump steps out of her motorcade vehicle as she departs Washington for a tour of several African countries from Joint Base Andrews, Maryland, U.S., October 1, 2018. (Photo by Carlo Allegri/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.

An inmate with a tattoo of Santa Muerte (The Saint of Death) reacts in the Topo Chico prison, during a media tour, in Monterrey, Mexico, February 17, 2016. The director of a prison in northeast Mexico where 49 people died in a riot this week was accused of murder and detained, along with two others, a state prosecutor said on Saturday. (Photo by Daniel Becerril/Reuters)

A guest poses with a magic wand during a soft opening and media tour of “The Wizarding World of Harry Potter” theme park at the Universal Studios Hollywood in Los Angeles, California in this picture taken March 22, 2016. (Photo by Kevork Djansezian/Reuters)