Here’s a lovely cutaway view of Hermannplatz station, at the intersection of what is now U7 (the lower platform here, running east-west) and U8 (the platform above, running north-south). 

The map also shows the pedestrian tunnels that connected the station directly with the basement of the monumental Karstadt department store, then one of the largest in the world. However – probably for reasons of clarity – the diagram places the entrance in the first basement level of the store and shows it as accessible by a bridge across the U7 tracks. In reality, the entrance was in the second (lower) basement level and crossed under the tracks via a tunnel. The Karstadt store was unfortunately blown up by the SS in 1945.

Source: berlin-hermannplatz.de