The closing of the gap in line U5 of the Berlin underground completes the missing connection between the Alexanderplatz and Brandenburger Tor stations. The existing line U5 currently ends at the Alexanderplatz. With the closure of the gap, the existing tunnels at the Berliner Roten Rathaus will be connected to the Brandenburger Tor station on the line U55. The project includes the construction of three new underground stations and two single‐track tunnels connecting them, which are being tunnelling by shield machines. The new alignment thus passes deep under the city, under the River Spree, the new Berliner Schloss and the Spreekanal as well as running along beneath the street Unter den Linden to the Brandenburger Tor. The construction activities are taking place right in the centre of Berlin and the particular local conditions are a logistical and technical challenge.