20. Beelitz-Heilstätten Hospital: Beelitz, Germany
What was once a tuberculosis clinic and a sanitarium, became a German military hospital during The Great War. Along with thousands of patients during that time, one of them was a young and hopeful Adolf Hitler. When World War I ended, the hospital returned to civilian use until World War II called it back into military use. During the course of the fighting, the Soviets took over the hospital until 1994, releasing it shortly after the fall of the wall.
19. Duga Radar: Siberia & Ukraine
Erected by the Soviets during the Cold War, the Duga radar system once served as early warning system for ballistic missiles. For thirteen years they did two things: keep the Soviets safe from unannounced attack and nothing since there never was an attack. Long since abandoned, these giant metal monstrosities still stand on the eastern side of Siberia and in the former Ukranian Soviet Republic. Seems like someone could repurpose them for a parkour workout center or something.