Four O'Clock Factoid is a daily feature on Track Twenty-Nine helping to get you through the workday with a bit of useless knowledge.
Geisterbahnhöfe (German: Ghost Stations) originally referred to closed subway stations in Berlin, through which trains passed without stopping due to the division of the city by the Berlin Wall. Some U-bahn or S-bahn lines ran for the most part in West Berlin, but passed through the Soviet Sector in the center of the city. Patrons could ride along these lines through East Berlin, but trains did not stop. The Geisterbahnhöfe were dimly lit and patrolled by East German border guards. Trains did stop at Friedrichstraße, which was a transfer point between Western lines and also a border crossing into East Berlin. The Western lines with Ghost Stations were today's U6 and U8 and the Nord-Süd Bahn of the S-bahn.
Here is a 1984 map of the U- and S-bahn networks produced by the Western operator, BVG. Geisterbahnhöfe are labeled as Bahnhöfe auf denen die Züge nicht halten (stations at which trains do not stop). On Eastern U- and S-bahn maps, West Berlin is depicted as having no infrastructure, and the Western lines passing through East Berlin are not shown. Here is an Eastern 1984 map.