Potsdamer Platz
The area of West Berlin adjacent to Potsdamer Platz then required a connection to the U-Bahn, and this need was eventually met by the construction of the M-Bahn, which used the abandoned U-Bahn platforms at Gleisdreieck and the U-Bahn tracks northwards towards the border. It then diverged slightly to the west to terminate close to Potsdamer Platz but still in West Berlin.