U4 (Berlin U-Bahn) · Relations URL: https://knowledge.ivjn.us/en/concepts/ubahn-berlin-u4/relation.html With 2.9 km and five stations, the U4 is the shortest line of the Berlin U-Bahn; it was opened on 1 December 1910 as Germany's first municipal U-Bahn and connects Nollendorfplatz with Innsbrucker Platz in Schöneberg. Page 1 / 0, 0 total