Engine driver Josef Kowatsch (top L) steers a train through the NEAT Gotthard Base Tunnel during a media visit near the town of Erstfeld August 24, 2015. Crossing the Alps, the world's longest train tunnel should become operational at the end of 2016, consisting of two parallel single track tunnels, each of a length of 57 km (35 miles). (Photo by Arnd Wiegmann/Reuters)

A couple covered in mud wait for it to dry at the Salt-works lakes near the Black Sea town of Burgas in Bulgaria on July 25, 2019. Thousands of tourists visit the red salt lakes for mud baths, which are believed to help the healing of muscular disorders and rheumatism. (Photo by Nikolay Doychinov/AFP Photo)

Revellers gather for the start of the Annual SantaCon Bar Crawl at Father Duffy Square, a section of Times Square, on December 14, 2019, in New York City. SantCon is an event where people make donations to charitable causes and dress up as a Christmas character and visit bars around the city. (Photo by Steven Ferdman/Getty Images)

British Prime Minister Boris Johnson visits the Pavegen stand, a company that converts footsteps into energy, at the Innovation Zone during the UK-Africa Investment Summit in London, Britain on January 20, 2020. (Photo by Leon Neal/Pool via Reuters)

People visit the Mansu Hill to lay flowers to the bronze statues of late leaders Kim Il Sung and Kim Jong Il on the occasion of the 108th birth anniversary of Kim Il Sung in Pyongyang, North Korea Wednesday, April 15, 2020. (Photo by Alamy Live News)

A clash has broken out among the police and the protesters on March, 25, 2021 against Indian prime minister Narendra Modi’s upcoming visit in Motijheel, Dhaka, Bangladesh. (Photo by Harun-Or-Rashid/ZUMA Wire/Rex Features/Shutterstock)

A Tibetan man stands nearby as a young tourist poses for photos on a white yak at the shore of the lake in Namtso in western China’s Tibet Autonomous Region, as seen during a government organized visit for foreign journalists, Wednesday, June 2, 2021. (Photo by Mark Schiefelbein/AP Photo)

People visit Luke Jerram's “In Memoriam”, a temporary memorial artwork for all those who lost their lives due to COVID-19, in Seaton Carew Park, Hartlepool, Britain on August 20, 2021. (Photo by Lee Smith/Reuters)