Passengers wait for a train to depart from the Hankou Railway Station in Wuhan, central China's Hubei province, Friday January 13, 2017. Officials expect that Chinese travelers will make almost 3 billion trips during the holiday travel rush that starts runs through Feb. 21. These trips include intercity flights, trains and local bus rides to villages for China's 1.4 billion people. (Photo by Chinatopix via AP Photo)

The waning moon sets behind leafless sumac trees on a crisp, clear morning, Thursday, December 15, 2016, in Portland, Maine. Much of the northern Mid-Atlantic and Northeast will stay cold for the next couple of days as the arctic air remains stuck over the northern Appalachians, the National Weather Service said. (Photo by Robert F. Bukaty/AP Photo)

Zulmira Jesus poses for a portrait at a street in Povoa de Agracoes, near Chaves, Portugal April 19, 2016. In the villages of Agracoes and Povoa de Agracoe, the steady drip-drip of emigration has brought down population numbers from more than 50 residents to fewer than a dozen each. These remaining villagers share the same glum acceptance that, after they have gone, their villages will die out too. It is the same desolate picture in scores of other backwater settlements in Portugal's interior, north to south. (Photo by Rafael Marchante/Reuters)

The sun rises beside St Mary's Lighthouse in Whitley Bay, Tyne and Wear, as the unseasonably cool weather continues on Thursday, April 28, 2016. (Photo by Owen Humphreys/PA Wire)

Wrestlers perform at an all female wrestling event in London. England on August 17, 2017. (Photo by Neil Hall/Reuters)

The battle by Jose Garcia, US. Category: bird behaviour. A great white heron (Ardea herodias occidentalis) fighting a green snake in the Florida Everglades. The fight lasted for nearly 20 minutes with the heron having to release its prey. (Photo by Jose Garcia/2017 Bird Photographer of the Year Awards)

To an outsider, their passion is at times illegal and often on the verge of life and death. But climbing rooftops of high-rise buildings and exploring abandoned facilities is in the blood of these young Muscovites. The small group calls itself “Rudex”, which stands for “roof and decay exploration”, and is akin a Western youth craze known as urbex or “urban exploration” of man-made structures. Here: Urban explorer Vad Him of Rudex team jumps whilst on a rooftop in Moscow, Russia, August 14, 2017. (Photo by Maxim Shemetov/Reuters)

Crowds supporting the Same Sеx Marriage Survey listen to politicians and advocates at Taylor Square in the heart of Sydney's gay precinct on November 15, 2017 in Sydney, Australia. Australians have voted for marriage laws to be changed to allow same-sеx marriage, with the Yes vote claiming 61.6% to to 38.4% for No vote. Despite the Yes victory, the outcome of Australian Marriage Law Postal Survey is not binding, and the process to change current laws will move to the Australian Parliament in Canberra. (Photo by James Alcock/Getty Images)