Page "Berlin S-Bahn" Paragraph 3

The S-Bahn routes all feed into one of three core lines: a central, elevated east-west line ( the Stadtbahn ), a central, mostly underground north-south line ( the Nord-Süd-Tunnel ), and a circular, elevated line ( the Ringbahn ).

Geographically, the Ringbahn takes the form of a dog's head and is colloquially known to Berliners by that name ( Hundekopf ).

Outside the Ringbahn, suburban routes radiate out in all directions.