At Hermannplatz station, which resembles something of an U-Bahn cathedral, the first underground rail–rail crossing in Berlin was developed; transfer to the GN-Bahn (later the "U8") was intended at this station. The station is also the first Berlin underground station to use escalators. The section from Hasenheide to Bergstraße (later "Karl-Marx-Straße") was put into operation on 11 April 1926. The final stage of the Neukölln branch at that time, the 1.5 kilometre-long (0.9 mi) extension to Grenzallee, was put into operation on 21 December 1930—the same day of the opening of what would become the U5 line—during one of the largest underground opening celebrations. Underground passengers could then travel from Seestraße (U6), through the city centre, to either Tempelhof or Grenzallee.