Pick a realistic royal Berlin route before you start walking: palace site, cathedral crypt, Museum Island, Unter den Linden, Brandenburg Gate and the Charlottenburg add-on.
Start at Schlossplatz, read the cathedral and Museum Island together, then walk Unter den Linden to Brandenburg Gate.
90 minutes
Best plan: walk the central axis first
For a first visit, this is the cleanest Hohenzollern Berlin route: palace site, Berliner Dom, Museum Island edge, Unter den Linden, Bebelplatz and Brandenburg Gate.
Start here because the old palace site explains the geography. Look from the palace facades toward the Berliner Dom, Museum Island and Unter den Linden before you move.