Roof-topping enthusiast Daniel Lau takes a selfie with high-rise buildings down below as he stands on the top of a skyscraper in Hong Kong, China on August 15, 2017. A craze that began in Russia has now taken hold in Hong Kong, one of the world's most vertical cities. Mr Lau said he had been inspired by Russian climbers and that he was unafraid of the vertiginous heights he scales. (Photo by ImagineChina/Rex Features/Shutterstock)

Expedition 44 flight engineer and NASA astronaut Scott Kelly seen inside the Cupola, a special module which provides a 360-degree viewing of the Earth and the International Space Station. Kelly is one of two crew members spending an entire year in space. (Photo by Scott Kelly/NASA)

A man exercises in the early morning on a hilltop overlooking Kabul, Afghanistan March 3, 2016. (Photo by Mohammad Ismail/Reuters)

An enterprising Chinese man pulls a bicycle cart packed high with bags of recyclable plastic containers in Shanghai July 25, 2002. The man sells each kilogram (2.2 pounds) of plastic for 0.08 yuan ($.01) to a nearby depot. (Photo by Claro Cortes IV/Reuters)

(L-R) Senior Drum Major Betts of the Scotts Guard, Bugler Lee Kidd, Guardsman Adam Deer of the Coldstream Guards and Lance corporal Michael Strong of the Princess of Wales's Royal Regiment pose in their full ceremonial attire at Wellington Barracks on March 21, 2012 in London, England. The group make up part of the ceremonial military personnel who will play a key role during Her Majesty the Queens Diamond Jubilee celebrations between June 2–5. (Photo by Dan Kitwood/Getty Images)

A group of Japanese schoolgirls marching in formation during a school visit to the third regiment to experience the soldier's way of life. (Photo by Fox Photos/Getty Images). Circa 1938

Suffering from a broken nose and bruised ribs Natasha Dzhuley, 16, relaxes after inhaling glue for the first time – something she swore she would never do, 2002. She was beaten by her pimps men in what Ruslana believes was a warning to other prostitutes to stay in line. Though another child believes her pimp had her beaten because she was pregnant. Less than a week after this picture of Natasha was taken she was dragged away by six men. She has not been heard or seen since. (Photo by Kurt Vinion /Getty Images)

An injured man is carried atop an Iraqi special forces armored vehicle during fighting against Islamic State militants in western Mosul, Iraq, Tuesday, March 14, 2017. (Photo by Felipe Dana/AP Photo)