People slide down a 1,082 feet (330 metre) long inflatable water slide in Hong Kong, China August 22, 2015. (Photo by Tyrone Siu/Reuters)

The 26th annual National Geographic Traveler Photo Contest is now accepting submissions. Official categories include: “Travel Portraits”, “Outdoor Scenes”, “Sense of Place” and “Spontaneous Moments”. The contest is accepting entries until June 30. Photo: “Forest lights”. Aurora Borealis over the forest of the Pyhae Luosto National Park, Finland. (Photo and caption by Nicholas Roemmelt/National Geographic Traveler Photo Contest)

Believers burn dried oak branches, which symbolizes the Yule log, on Orthodox Christmas Eve in front of the St. Sava temple in Belgrade, Serbia, January 6, 2016. Serbian Orthodox believers celebrate Christmas on January 7, according to the Julian calendar. (Photo by Marko Djurica/Reuters)

Australia's Jessica Lim competes in the women's nangun final during the 13th World Wushu Championship 2015 at Istora Senayan stadium in Jakarta, November 17, 2015. (Photo by Reuters/Beawiharta)

In this June 23, 2015 photo, Ashaninka Indian beauty contestants pose for a photo with members of a visiting music group, hired to perform during the annual founding anniversary festivities, in Otari Nativo, Pichari, Peru. The contestants wear the simple brown dresses of the Ashaninka woman, their faces dotted in a traditional design with a red dye extracted from a spice called achiote. (Photo by Rodrigo Abd/AP Photo)

Gold medallist Rachelle Simpson of the U.S. celebrates after the women's 20m high dive competition during the Aquatics World Championships in Kazan, Russia August 4, 2015. (Photo by Hannibal Hanschke/Reuters)

A close up shows Ukraine's Hanna Ryzhykova leg breaking a hurdle before crashing out as she competes in the women's 400m hurdles heats during the European Athletics Championships at the Letzigrund stadium in Zurich on August 13, 2014. (Photo by Olivier Morin/AFP Photo)

Runners cross the Verrazano-Narrows Bridge shortly after the start of the New York City Marathon in New York, November 2, 2014. (Photo by Lucas Jackson/Reuters)