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)

Giant panda Xiao Qi Ji plays at his enclosure at the Smithsonian National Zoo in Washington, Thursday, September 28, 2023. (Photo by Jose Luis Magana/AP Photo)

Horses eat hay and rest on straw at a stud farm in Wehrheim near Frankfurt, Germany, Tuesday, December 5, 2023. (Photo by Michael Probst/AP Photo)

A model stands in a light backstage after presenting the collection by Russian designer Alena Akhmadullina at The Russian State Library, one of the three national libraries of Russia, the largest library in the country, largest in Europe, in Moscow, Russia, on Wednesday, November 29, 2023. (Photo by Alexander Zemlianichenko/AP Photo)

Aidan Thomas wears a Smokey Bear t-shirt as he watches smoke from the Airport Fire rise behind Meander Lane in Trabuco Canyon, Calif., on Monday, September 9, 2024. (Photo by Jeff Gritchen/The Orange County Register via AP Photo)

Black-headed gulls sit on pickets at a riverside in Tokyo, Japan, December 27, 2015. (Photo by Toru Hanai/Reuters)

Bullet the bulldog skateboards in a seafront area in the city of Vladivostok, on Russia's Pacific coast on August 9, 2021. The 6-year-old dog learnt how to skateboard two years ago thanks to his owner, Sergei Shukshuyev. (Photo by Yuri Smityuk/TASS)

Bollywood actress Sushmita Sen walks the ramp to showcase the creation of designer Sunita Shanker during Lakme fashion week winter 2018 in Mumbai, India, Thursday, August 23, 2018. (Photo by Rajanish Kakade/AP Photo)