The U1 line runs from Kreuzberg to Charlottenburg boroughs in Berlin, Germany. The line is nearly 9 km long and currently has 13 stations. Construction started on this line in the late 1800s and portions of the U1 are some of the oldest parts of the Berlin U-Bahn system.
The U1 affords great views of the city as portions of it snake above ground through the borough of Kreuzberg. Originally, the U1 line was planned for a different street altogether, it wasn’t until wealthy residents complained that the line was moved to its current location.
This line has a few of my favorite stations. Schlesisches Tor has Burgermeister located underneath it in an old city toilet building, my vote for best burger in Berlin. Wittenbergplatz is another great station, like stepping into a time machine.
Eventually, the U1 line may be extended in the east to Frankfurter Tor (U5) U-Bahn station, although with the existing (excellent) tram connection, it is unclear why this would be worth the money.
Construction work is currently occurring on this line and if you’re very new to Berlin, you may be more familiar with the temporary line U12, which combines the U1 and U2 lines.