Two days covers Berlin's essentials, but the city is huge and spread out, so 48 hours is a rush and you will move fast between districts. In two days you can do the historic Mitte core on day one, the Brandenburg Gate, Reichstag dome, Holocaust Memorial, Museum Island, and Gendarmenmarkt, then give day two to the Wall and Cold War story, Checkpoint Charlie, Topography of Terror, and the East Side Gallery, ending with a Kreuzberg dinner. What you must cut: Charlottenburg, Prenzlauer Berg, Tempelhofer Feld, the lakes, and any slow neighborhood time, so this is a highlights tour, not a Berlin you get to know. It suits a weekend break or a first taste before combining with Prague. The non-negotiables: register online for your free Reichstag dome slot before you fly, and buy an ABC day ticket the moment you land, controls are frequent and fines steep. Base in Mitte so both mornings start near the sights. A third day is the single best upgrade, and Berlin really wants it.