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 model prepares backstage at the Meskita fashion show during Mercedes-Benz Fashion Week Spring 2015 on September 4, 2014 in New York City. (Photo by Larry Busacca/Getty Images for Meskita)

These adrenaline-junkie climbers go to extraordinary lengths, and heights, to take a selfie. Hundreds of metres above the ground, the climbers risk their life and liberty as they scale huge structures and photograph the results. Known as urban exploration, the aim is to find extremely high and almost inaccessible city buildings and reach their dizzying summits. (Photo by Yaroslav Segeda/Solent News)

A man stands beside the Philippine flag as colorful umbrellas adorn a village hall in suburban San Juan, east of Manila, Philippines, on June 27, 2013. (Photo by Aaron Favila/Associated Press)

A man wears a sweater covered in Irish themed pins as he stands with thousands of spectators to watch the 254th New York City St. Patrick's Day parade up 5th Avenue in the Manhattan Borough of New York, March 17, 2015. (Photo by Mike Segar/Reuters)

In this April 14, 2018 photo, National Ballet of Cuba dancer Daniela Gomez Perez stands on point as she poses outside the Capitol in Havana, Cuba. Gomez, who says Cubans love dancing, trusts the next generation of leaders will continue such traditions and that art will continue to be the engine of Cuban society. Gomez said she is proud to represent Cuba during a dance trip in May to Washington, Tampa and Chicago, and that the Cuban state has always supported dance. (Photo by Ramon Espinosa/AP Photo)

A Russian army conscript called up for service in the Kremlin regiment and a woman say farewell at Yekaterinburg-Passazhirsky railway station in Yekaterinburg, Russia on November 15, 2018. (Photo by Donat Sorokin/TASS Russian News Agency)

The Leshan Giant Buddha, a 71-metre tall stone statue, is carved out of a cliff face in the southern part of Sichuan province in China. (Photo by Suchet Suwanmongkol/500px)