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)

The winner of the Miss Tattoo Brazil 2014 contest, Bruna Barros, shows a tattoo that says 'My body, my rules' during Tattoo Week, the largest convention of art in the skin of Latin America, in Sao Paulo, Brazil, 14 July 2017. A tattooed woman beauty pageant, the new trends and techniques of the tattoo world, body piercing and the environment of the art of definitively painting the body, are all due to be addressed during the seventh edition of the “Tattoo Week Sao Paulo“. (Photo by Sebastiao Moreira/EPA)

Handler Jorge Garcia-Bengochea holds Honor, a miniature therapy horse from Gentle Carousel Miniature Therapy Horses, as they visit with patients at the Kravis Children's Hospital at Mount Sinai in the Manhattan borough of New York City, March 16, 2016. Some of the most powerful medicine delivered to young patients at Mount Sinai Hospital in New York on Wednesday came in a package less than 32 inches tall and with a tail. Honor, a 10-month-old colt with Gentle Carousel Miniature Therapy Horses, trotted into the hearts of dozens of children and teens being treated at the Manhattan hospital. (Photo by Mike Segar/Reuters)

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 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)

U.S. Marines kick in a door while securing a building next to the main hospital in central Baghdad April 15, 2003, which will be used as a temporary Iraqi police headquarters. (Photo by Jerry Lampen/Reuters)

The Queen Elizabeth Tower (Big Ben) is reflected in a puddle as a cyclist rides by in London, on 27 June 2016. Britain began preparations to leave the European Union on Monday but said it would not be rushed into a quick exit, as markets plunged in the wake of a seismic referendum despite attempts to calm jitters. (Photo by Leon Neal/AFP Photo)

The Guinness World Record for the fastest tortoise in the world is held by Bertie, a South African leopard tortoise, who covered 5.49 metres in 19.59 seconds. (Photo by Paul Michael Hughes/Guinness World Records/PA Wire Press Association)