Two young women, having enjoyed a drink at a party, dance together in Tehran, Iran. Although unrelated men and women are forbidden to socialise together many people ignore these strictures in the privacy of their own homes. (Photo by Hossein Fatemi/Reuters/Panos Pictures/Courtesy of World Press Photo Foundation)

Farmers clash with riot policemen during a protest outside the Greek Agriculture Ministry on March 8, 2017 in Athens, Greece. Two people were detained after the windows of two police vans were smashed as approximately 1,000 farmers, mainly from the island of Crete, took part in the protest. (Photo by Nikolas Georgiou/ZUMA Wire/Rex Features/Shutterstock)

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)

Two girls wearing traditional Sevillian dresses talk during the “Feria de Abril” (April Fair) in Sevilla on April 30, 2017. The fair dates back to 1847 when it was originally organized as a livestock fair but has turned into a week of flamenco dancing, music and bullfighting. (Photo by Cristina Quicler/AFP Photo)

The Eiffel Tour-the body language of balance. I came across this group of young adults from Sarajevo, Bosnia, having fun testing their balance two nights ago in on the Esplanade de Trocadero. (Photo and comment by Peter Turnley)

A man watches the approaching flames as the Springs fire continues to grow near Camarillo, California, on May 3, 2013. The wildfire has spread to more than 18,000 acres on day two and is 20 percent contained. (Photo by David McNew)

A truck is seen in a hole after part of the structure of a bridge collapsed into a river in Changchun, Jilin province May 29, 2011. Two truck passengers were injured, while the cause of the accident is still under investigation, local media reported. (Photo by Reuters/China Daily)

A wounded protester is attended before being rushed to a vehicle following violence in Independence Square in Kiev February 20, 2014. Ukrainian protesters seized back Kiev's Independence Square in fresh clashes with riot police on Thursday that left several injured and possibly two demonstrators dead. (Photo by Konstantin Chernichkin/Reuters)