On May 28, 1987, a young German named Matthias Rust was able to land his Cessna plane inside the Soviet Union, in Moscow's Red Square. Rust was only 19. He flew from Finland to Moscow and was several times tracked by Soviet radar -- yet, he was never engaged, and remarkably, was not shot-down. He landed and a surprised crowd of curious onlookers greeted him; he was then quickly arrested, given a trial, and sentenced to four years in a Soviet prison (he served just over one full year).
The incident was damaging to the reputation of the Soviet Military -- they had claimed their defenses were unable to be penetrated. Two years later would see the collapse of the Berlin Wall, dividing West and East Germany, and in 1991 "Soviet" Russia would follow.