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)

Asia Sawicka as Anastasia IV poses for a photograph prior to a rehearsal of the Circus of Horrors' latest show Voodoo, ahead of Halloween, at the Wookey Hole Caves Theatre near Wells on October 19, 2017 in Somerset, England. (Photo by Matt Cardy/Getty Images)

Archive: A group of people dressed as Santa Claus wait for the bus on December 1960, London, England. (Photo by Keystone-France/Gamma-Keystone via Getty Images) Modern Day: Passengers wait for busses in Holborn on November 24, 2017 in London, England. (Photo by Chris J. Ratcliffe/Getty Images)

A woman plays with her three dogs at the beach after sunset in Del Mar, California, USA on November 10, 2017. (Photo by Mike Blake/Reuters)

Revellers enjoy themselves during Hogmanay celebrations in Edinburgh, Scotland on December 31, 2017. (Photo by Russell Cheyne/Reuters)

A visitor poses for a picture during Sao Paulo Fashion Week in Sao Paulo, Brazil, March 16, 2017. (Photo by Nacho Doce/Reuters)

A robot named “Robovie-II”, developed by Japanese robotics research institution ATR, moves around at a grocery store during a shopping assisting experiment by utilizing the robot in an ubiquitous network technology platform in Kyoto, western Japan January 6, 2010. (Photo by Yuriko Nakao/Reuters)

Members of the Mayossa Folk Dance Group pour water on young women in Kiskunmajsa, some 140 kms southeast of Budapest, Hungary, Monday, April 2, 2018. According to a several hundred years old tradition of Hungarian villages young men pour water on young women who in exchange present their sprinklers with beautifully colored eggs on Easter Monday. (Photo by Sandor Ujvari/MTI via AP Photo)