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 Tibetan woman with horses in a remote area of the Yushu Autonomous Prefecture of the Tibetan Plateau on May 31, 2016. (Photo by Giulia Marchi/The Washington Post)

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)

Local residents evacuate onto a street minutes after an earthquake in central Kathmandu, Nepal, May 12, 2015. A 7.3 magnitude earthquake killed at least 37 people and spread panic in Nepal on Tuesday, bringing down buildings already weakened by a devastating tremor less than three weeks ago and unleashing landslides in Himalayan valleys near Mount Everest. The earthquake was centered 76 km (47 miles) east of the capital in a hilly area close to the border with Tibet, according to coordinates provided by the U.S. Geological Survey. (Photo by Athit Perawongmetha/Reuters)

Daniela Burza, 45, wears a Nasty Woman t-shirt and a mask of U.S. Democratic presidential nominee Hillary Clinton as she competes during the Haunted Heats Halloween Surf Contest in Santa Monica, California, U.S., October 29, 2016. (Photo by Lucy Nicholson/Reuters)

(L-R) Recording artists Jessie J, Ariana Grande, and Nicki Minaj perform onstage during the 2014 MTV Video Music Awards at The Forum on August 24, 2014 in Inglewood, California. (Photo by Michael Buckner/Getty Images)

Steam enthusiasts demonstrate their engines at the Great Dorset Steam Fair, the biggest event of its kind in Europe on September 2, 2011 in Tarrant Hinton, near Blandford, England. Over 200,000 people are expected to attend the 600 acre event, which is in its 43rd year and includes displays and demonstrations of steam and vintage machinery over five days. (Photo by Matt Cardy/Getty Images)