Vietnam’s Son Doong cave, the largest in the world, could hold a 40-story skyscraper inside. The pristine ecosystem has its own river and jungle. Despite its size, Son Doong wasn’t discovered until 1991. It was lost again for nearly two decades and was fully explored for the first time in 2009. (Photo by Jason Speth/HuffPost)

Spectators cheer after Medina Spirit, ridden by John Velazquez wins 147th Kentucky Derby at. Churchill Downs, in Louisville, Kentucky, U.S. May 1, 2021. (Photo by Bryan Woolston/Reuters)

A woman enjoys the sun at Plaka beach on the Aegean island of Naxos, Greece, Friday, May 14, 2021. Greece launched its tourism season Friday amid a competitive scramble across the Mediterranean to lure vacationers emerging from lockdowns. (Photo by Thanassis Stavrakis/AP Photo)

The first autonomous and electric shuttle of PostAuto Schweiz in the old village of Sion, Switzerland, June 2016. (Photo by Ruben Sprich/Reuters)

A small flock of birds seems to be giving an escort to an airliner on final approach to Reagan Washington National Airport in Arlington, Virginia on January 12, 2022. The scene took place over Gravelly Point which is an area within the National Park Service's George Washington Memorial Parkway. (Photo by Michael S. Williamson/The Washington Post)

A wax figure of U.S. actress Scarlett Johansson stands outside Madame Tussauds New York attraction shortly after the figure was unveiled in Times Square in New York, July 30, 2015. (Photo by Mike Segar/Reuters)

The Royal Castle is seen a veil of heavy winter smog in Budapest, Hungary on January 30, 2017. (Photo by Laszlo Balogh/Reuters)

A reveller performs while attending the block party “Galo da Madrugada” during carnival festivities in Sao Paulo, Brazil on February 25, 2020. (Photo by Rahel Patrasso/Reuters)