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Pic related is a "ghost station" which has never been in use. It is right under the underground light rail station at Hannover Central Station (Hauptbahnhof).
The station is the result of some advance construction work that had been done before routing plans for the city center were changed. It was supposed to be served by present-day lines 10 and 17, perpendicular to the light rail platforms above. But lines 10 and 17 never got the inner-city tunnel that they deserved and spent more than 40 years in limbo before different plans were made.
You can visit these station occasionally during guided city tours.