One day in Berlin is enough to cover its defining sights if you move with purpose, so this itinerary skips the museums that reward slower visits and the outer neighborhoods entirely. Instead it links the historic core along Unter den Linden with the city's Cold War landmarks in one walkable loop.
Start early at the Brandenburg Gate before the crowds build, then walk a few minutes to the Reichstag Building to see its glass dome from outside, and pause at the nearby Holocaust Memorial. Mid-morning, stroll down Unter den Linden toward Museum Island, stopping at the Berlin Cathedral and choosing just one museum, the Pergamon Museum, since there is only time for one. For lunch, head toward Alexanderplatz and visit the DDR Museum for a fast, engaging look at everyday life under communism. In the afternoon, take the U-Bahn or a taxi to the Berlin Wall Memorial on Bernauer Strasse to understand the wall's history, then continue to the East Side Gallery to walk along its longest surviving, mural-covered stretch. As evening falls, make your way back toward the Kaiser Wilhelm Memorial Church for a striking contrast between its bombed ruin and modern tower, then close the day with dinner nearby.