Watch Cities of the Underworld Season 2 Episode 13 Online

Deep within the former Soviet Union lies a classified, subterranean world of Cold War secrets. In Ukraine, which once had the world's third largest nuclear arsenal, Don ducks behind the Iron Curtain to reveal a how the Soviets were really preparing for a Nuclear War. From nuclear submarine bases to underground apartment blocks, these sites are so top-secret, they've never before been seen on American television.