Stunning silhouettes under European cities reveal the size and splendor of the continent’s urban foundations. Photographer and content-manager Anna Arinova, 28, from Moscow, captured the awe-inspiring labyrinths in Russia and Germany. Here: Regenwurmlager, Poland. The Regenwurmlager is an extensive underground fortification area constructed by Germany in 1920s-1940s, now in western Poland, near the city of Międzyrzecz. (Photo by Anna Arinova/Caters News)

A student from the General Yermolov Cadet School takes part in weapons training during a two-day field exercise near the village of Sengileyevskoye, just outside the south Russian city of Stavropol April 13, 2014. The General Yermolov Cadet School in the southern Russian city of Stavropol is a state-run institution that teaches military and patriotic classes in addition to a normal syllabus. (Photo by Eduard Korniyenko/Reuters)

Visitors check photos on a smartphone during the activity "Birgu by Candlelight" in the medieval city of Birgu, also known as Vittoriosa, outside Valletta, Malta, October 10, 2015. During the annual event, most street lights are switched off and the city is lit up by candlelight, creating a magical ambience, according to its local council. (Photo by Darrin Zammit Lupi/Reuters)

A workman takes a siesta on a girder during the building of Radio City, the city of New York spread out below. (Photo by General Photographic Agency/Getty Images). Circa 1933

Fighters battle in Manhattan's Union Square during a massive pillow fight on April 2, 2011 in New York City. Over 130 cities worldwide are participating in the fourth annual International Pillow Fight Day. (Photo by Mario Tama/Getty Images)

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

Injured horses huddle together in Oklahoma City on Monday. (Photo by Chris Landsberger/The Oklahoman)