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)

A publican serves a glass of stout to a donkey in the East End of London, 1960s. (Photo by Steve Lewis/Getty Images)

Gray whale feeding at the surface and showing it's baleen. (Photo by Christopher Swann/Biosphoto)

“These Rajasthani sisters were sitting on the staircase inside their house relaxing and enjoy a cup of masala chai”. (Photo by Firdaus Hadzri/National Geographic Travel Photographer of the Year Contest)

Ellesse Janda welcomes a spring rainbow at Cresswell in Northumberland, United Kingdom on March 17, 2023. (Photo by Ian Sproat/Picture Exclusive)

A row of abandoned oil tanks is filled with creepers on the riverside of Liyun River in Huai 'an, East China's Jiangsu Province, May 9, 2023. (Photo credit should read CFOTO/Future Publishing via Getty Images)

Children walk amid a mirror installation titled “Sea of Mirrors”, featuring digital images of fish in the ocean during a preview tour the day before the show's public opening at the AquaRio aquarium in Rio de Janeiro, Brazil, Wednesday, June 14, 2023. (Photo by Silvia Izquierdo/AP Photo)

The artist Luke Egan, also known as Filthy Luker, gets Horrible Harvey, his inflatable monster on October 26, 2022, pumped up for his debut at the annual Halloween in the City celebrations in Manchester, United Kingdom this weekend. (Photo by Dominic Lipinski/PA Wire Press Association via Getty Images)