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)

Wrestlers perform during an all-female wrestling event on International Women's Day at the Resistance Gallery in Bethnal Green on March 8, 2019 in London, England. (Photo by Jack Taylor/Getty Images)

A photo from Madonna’s high school yearbook at her childhood home in Rochester, Michigan, circa 1973. (Photo by Rebel Images/Rex Features/Shutterstock)

Alexandre Vinokourov of Kazakhstan from the T-Mobile Team is chased by eccentric german inventor Didi Senft dressed as the red devil during the stage 16 of the 92nd Tour de France between Mourenx and Pau on July 19, 2005, France. (Photo by Friedemann Vogel/Bongarts/Getty Images)

A young girl navigates her way around Hampton Court maze in the spring sunshine on May 2, 2009 in London, England. The Hampton Court maze is one of the most famous hedge mazes in the world and was planted between 1689 and 1695 by George London and Henry Wise. (Photo by Dan Kitwood/Getty Images)

Egyptian President Hosni Mubarak speaks to the media after talks with German Chancellor Angela Merkel at the Chancellery on April 23, 2008 in Berlin, Germany. (Photo by Sean Gallup/Getty Images)

Riot police walk in the street as a couple kiss on June 15, 2011 in Vancouver, Canada. Vancouver broke out in riots after their hockey team the Vancouver Canucks lost in Game Seven of the Stanley Cup Finals. (Photo by Rich Lam/Getty Images)