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)

Dogs and owners run during of 4k pet run “A Race with a Cause”, organized to raise funds for a shelter for rescued dogs in Caracas, Venezuela, Sunday, April 30, 202. (Photo by Ariana Cubillos/AP Photo)

A dog sits in a plastic basin filled with water in Taipei, Taiwan, 05 May 2018. Betel nut seller Mr Luo, the dog's owner, said he puts his dog Ah Dai (Stupid Guy) in the water-filled basin whenever the weather get hot. Luo has a dozen pairs of glasses for Ah Dai, so the dog wears different glasses every day and many tourists take photos of Ah Dai. (Photo by David Chang/EPA/EFE)

A dog dressed as Oscar the Grouch takes part in the annual halloween dog parade at Manhattan's Tompkins Square Park in New York, NY, U.S. on October 21, 2017. (Photo by Lucas Jackson/Reuters)

One of ten little spotted kiwi is released on Motuihe Island, a conservation pest-free island close to Auckland, on March 21, 2009 in Auckland, New Zealand. Eventually up to 40 endangered kiwi birds will be relocated to the island. (Photo by Hannah Johnston/Getty Images)

Beekeeper and Chairman of The London Beekeepers Association John Chapple installs a new bee hive on an urban rooftop garden in Hackney on July 1, 2009 in London, England. (Photo by Dan Kitwood/Getty Images)

Entertainers from the She Huo cultural troupe rehearse for the Edinburgh Military Tattoo at Redford barracks on August 5, 2009 in Edinburgh, Scotland. (Photo by Jeff J Mitchell/Getty Images)

Skeleton bodypainting in Chimbu tribe. Village Mindima, Simbu (a Highlands Region province in Papua New Guinea), September 14, 2009. (Photo by Rita Willaert; Source: Flickr)