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)

Participants of the “Lady in red“ procession, marking the day of the Summer Solstice, walk on a promenade of the Yenisei River in Krasnoyarsk, Russia on June 22, 2019. (Photo by Ilya Naymushin/Reuters)

A man walks on a slackline during the 7th edition of the European “Marmotte Highline Project” (MHP) festival in Lans-en-Vercors, near Grenoble, eastern France, on July 4, 2019. The event, during which the participants will be able to evolve on the various highlines located in the Regional Natural Park of Vercors, takes place until July 7, 2019. (Photo by Philippe Desmazes/AFP Photo)

A plane flies past the moon in west London on Monday, January 17, 2022. The first full moon – the Wolf moon according to native north Americans – of 2022. (Photo by Victoria Jones/PA Images via Getty Images)

Migratory flamingos arriving from Europe are seen in Port Fouad Nature Reserve, on the outskirts of Port Said Governorate, Egypt on December 12, 2022. (Photo by Mohamed Abd El Ghany/Reuters)

Big waves approach the beach of Nazare, Portugal, Tuesday, March 26, 2024. The high waves were caused by strong winds at one of the world's most popular surf spots. (Photo by Michael Probst/AP Photo)

A visitor walks past an installation artwork entitled “Confuciuse” which combines the word “Confucius” and “confuse” in the contemporary art exhibition at “Fun and Art” Festival on December 13, 2008 in Xian of Shaanxi Province, China. (Photo by China Photos/Getty Images)

Elephants spray tourists with water in celebration of the Songkran water festival in Thailand's Ayutthaya province, about 80 km (50 miles) north of Bangkok, April 9, 2014. (Photo by Rungroj Yongrit/EFE)