Crossing the inner German border

Crossing the inner German border between East and West Germanies remained possible throughout the Cold War; it was never as thoroughly sealed in the fashion of the border between the two Koreas, though there were severe restrictions on the movement of East German citizens. The post-war agreements on the governance of Berlin specified that the Western Allies were to have access to the city via defined air, road, rail and river links.

Source: Wikipedia — Crossing the inner German border (CC BY-SA 4.0)