Create a realistic animation starting in a gritty urban environment, swiftly navigating through streets lined with graffiti, posters, and flickering lights. Transition to a rugged, dimly-lit passage lined with cables, echoing mechanical sounds, and occasional flickers of light. Descend into a meticulously detailed atomic bunker hidden deep beneath the city, featuring thick concrete walls, reinforced steel doors with heavy bolts, vintage control rooms equipped with analog gauges and switches, and period-specific military signage. Capture the solemn atmosphere of the Cold War era with authentic textures and realistic visuals, emphasizing the stark contrast between the chaotic surface world and the structured, purposeful interior of the bunker.