A picture rotated 180 degrees shows visitors walking inside an “Upside-down House” attraction at the VVTs the All-Russia Exhibition Center in Moscow, on January 14, 2014. The attraction to experience a new perspective of a house standing upside down was opened first time in Russia, the show organisers said. (Photo by Alexander Nemenov/AFP Photo)

Tourists ice skate at night on the Eiffel Tower's skating rink in Paris December 9, 2014. The skating rink, located on the first level of the Eiffel Tower, opens to the public as part of the Christmas holiday season. (Photo by Charles Platiau/Reuters)

A girl rides on a train as she takes part in the first edition of the No Pants Subway Ride in Bucharest, Romania, Sunday, January 11, 2015. The No Pants Subway Ride is an annual which was started in 2002 by Improv Everywhere in New York, the goal is for riders to get on the subway train dressed in normal winter clothes without pants and keep a straight face. (Photo by Vadim Ghirda/AP Photo)

Polar bear twins make their first public appearance with their mother “Freedom” at Ouwehands Zoo Rhenen, in Rhenen, The Netherlands, 19 February 2015. The twins, who were born in November 2014, have not been named because their gender has not yet been determined. (Photo by Bart Maat/EPA)

Models of the “Altyr” fashion theatre, dressed in Khakas national costumes, get over a wooden fence during a photo session, as a part of the rehearsal for the Tun-Pairam traditional holiday (The Holiday of the First Milk) celebration at a museum preserve outside Kazanovka village near Abakan in the Republic of Khakassia, Russia, May 28, 2016. (Photo by Ilya Naymushin/Reuters)

A gravedigger competes as a boy looks on during the first National Grave Digging competition at the public cemetery of Debrecen, 226 km east of Budapest, Hungary, Friday, June 3, 2016. Eighteen two-man teams of Hungarian gravediggers are demonstrating their skills for a place in a regional championship to be held in Slovakia. (Photo by Zsolt Czegledi/MTI via AP Photo)

An Afghan Army soldier secures the hill overlooking the Kart-e Sakhi mosque in Kabul, Afghanistan, Wednesday, March 20, 2013. Thousands of Afghans will celebrate Nowruz on Thursday, March 21, 2013 to mark the first day of spring and the beginning of the year on the Iranian calendar. (Photo by Ahmad Jamshid/AP Photo)

“Aurora Hunters”. Photographers taking part in a photography tour on the Lofoten Islands in Norway, pull over on the side of the road to take a photo of their first ever Aurora Borealis after spotting it from their tour bus. Photo location: Rystad, Lofoten Islands, Norway. (Photo and caption by Mark Gee/National Geographic Photo Contest)