There's a wall in Berlin that separates it from Berlin. It's not the wall you're thinking of, but it's still symbolic of the cold war that sets the stage for the fascinating science fiction series, COUNTERPART.
Several years ago, an experiment went wrong, and suddenly where there was once one dimension there were now two, each of them identical up to that point in time, and now able to diverge in minute ways, each change cascading into more, like the flap of butterfly wings contributing to the hurricane. The bridge between these two Earths is below the building that is now a United Nations outpost, run by an organization that exists to keep the other dimension a secret, while controlling immigration between the sides, carrying out diplomatic gestures, and engaging in espionage.