Andrey Karr from Western Riders Slacklines at sunset above big waves in Nazare, Portugal on December 27, 2017. (Photo by Aidan Williams/National Geographic Travel Photographer of the Year Contest)

Surfer Arlen Macpherson sits on his board, which has an electronic shark repellent device installed, at Sydney's Bondi Beach in Australia, August 18, 2015. A spate of shark attacks in Australia has left some of world's top surfing beaches deserted and many people having second thoughts about taking a swim as the summer approaches. Macpherson paid A$390 for a device embedded in his surf board to repel sharks by emitting an electronic force field that overpowers its sensing organs. (Photo by David Gray/Reuters)

A combination picture shows participants in costume at a Halloween parade in Kawasaki, south of Tokyo, October 25, 2015. More than 100,000 spectators turned up to watch the parade, where 2,500 participants dressed up in costumes, according to the organiser. (Photo by Yuya Shino/Reuters)

Jason Derulo (C) performs “Get Ugly” at the People's Choice Awards 2016 in Los Angeles, California January 6, 2016. (Photo by Mario Anzuoni/Reuters)

The Disney Fantasy cruise ship is docked for its christening on March 1, 2012 in New York City. (Photo by Jamie McCarthy/Getty Images)

Boys play with a drainage culvert used for flood control in Las Pinas, Metro Manila February 28, 2016. (Photo by Erik De Castro/Reuters)

Iggy Azalea shares a joke with Andy Lee and Hamish Blake during Bonds 100th birthday celebration event at Cafe Sydney on August 19, 2015 in Sydney, Australia. (Photo by Brendon Thorne/Getty Images)

Hospitality staff members laugh as they stand on Tiananmen Square before the closing ceremony of China's 19th Party Congress at the Great Hall of the People in Beijing, Tuesday, October 24, 2017. The ruling Communist Party on Tuesday formally lifted Xi Jinping's status to China's most powerful ruler in decades, setting the stage for the authoritarian leader to tighten his grip over the country while pursuing an increasingly muscular foreign policy and military expansion. (Photo by Mark Schiefelbein/AP Photo)