Russian servicemen look on as a Mi-24 helicopter fly overhead during the Open Water competition for pontoon bridge units, as part of the International Army Games 2018, outside Murom, Russia August 3, 2018. (Photo by Maxim Shemetov/Reuters)

A handout photo made available by Limex Images of Pete McLeod of Canada (R) and Kirby Chambliss of the United States flying over the city of Kazan prior to the fifth stage of the Red Bull Air Race World Championship in Russia on August 22, 2018. (Photo by Joerg Mitter/EPA/EFE/Limex Images)

Manson Gerasimov of Russia and Agustina Piaggio of Argentina, representing the city of Rio Grande, Argentina, perform during the Stage style final round at the Tango World Championship in Buenos Aires, Argentina on August 23, 2018. (Photo by Marcos Brindicci/Reuters)

A skier in a festive costume attempts to cross a pool of water at the foot of a ski slope while competing in the annual Gornoluzhnik amateur event to mark the end of the ski season at the Bobrovy Log ski resort in the suburbs of the Siberian city of Krasnoyarsk, Russia, April 14, 2019. (Photo by Ilya Naymushin/Reuters)

Servicewomen march in formation during a Victory Day military parade marking the 74th anniversary of the victory over Nazi Germany in the 1941-1945 Great Patriotic War, the Eastern Front of World War II, in Moscow's Red Square, Russia on May 9, 2019. (Photo by Valery Sharifulin/TASS)

Audrey Lu and Misha Mitrofanov of the United States compete in the Pairs Short Program during day 1 of the ISU Grand Prix of Figure Skating Rostelecom Cup at Megasport Arena on November 15, 2019 in Moscow, Russia. (Photo by Maxim Shemetov/Reuters)

Womentake a selfie in front Russian military vehicles during a rehearsal for the WWII Victory Parade in Moscow on June 17, 2020. Russia's President Putin on June 24 will preside over a massive military parade to mark Soviet victory in World War II, which was postponed due to the coronavirus pandemic. (Photo by Dimitar Dilkoff/AFP Photo)

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)