The easternmost stretch of the U1 is, according to rbb, the Berlin U-Bahn's oldest stretch of track. As such, it's set to be cleaned and updated during a 3-week closure in Spring 2018, following on the heels of two other major weeks-long closures (the U7 and the southern Ringbahn).
Between Gleisdreieck and the line's eastern terminus at Warschauer Straße, the U1 runs on elevated tracks, offering a continuous view of the city from both sides of the train. These older lines use the corresponding older "small-profile" trains also used on the U3, U4, and U6, among others, as opposed to the "large-profile" trains that run on the U7. The tracks wind through Kreuzberg and over the Oberbaumbrücke before stopping at Warschauer Straße, itself being rebuilt as a true single-station connection between U- and S-Bahn.
This video begins at Kottbusser Tor, passing through Görlitzer Bahnhof and Schlesische Straße and crossing the Oberbaumbrücke before ending at Warschauer Straße.