Berlin Hauptbahnhof
The latest line to open is U55 from Berlin Hauptbahnhof to Brandenburger Tor, on 8 August 2009. This line was extended on 4 December 2020, to Alexanderplatz, where it connects with the U5 to Hönow, creating three new stations in the city center: Berliner Rathaus, Museumsinsel and Unter den Linden.