Key Points:
Berlin is the one of the top cities to visit in the world.
Earth Trekkers has provided a pretty good travel guide for Berlin.
The primary things to do in Berlin include: Museum Island (1 day), the Berlin Wall and Berlin Wall Memorial (1 day), Teufelsberg and Charlottenburg Palace (1 day).
According to Wikipedia, "Berlin is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits." "Berlin contains three World Heritage Sites: Museum Island; the Palaces and Parks of Potsdam and Berlin; and the Berlin Modernism Housing Estates. Other landmarks include the Brandenburg Gate, the Reichstag building, Potsdamer Platz, the Memorial to the Murdered Jews of Europe, the Berlin Wall Memorial, the East Side Gallery, the Berlin Victory Column, Berlin Cathedral and the Berlin Television Tower, the tallest structure in Germany."
Here we quote the best way to travel in Berlin provided by Earth Trekkers, a very good travel website created by an around-the-world traveler.
Check ChatGPT's answer for alternative itinerary.