Berlin: you cannot possibly not visit the Jewish Museum. It's adjacent to the Alexanderplatz which any literary minded traveller should visit, although it has changed an awful lot since Döblin's time. There are, I gather, guided tours which explain the changes. The StaSi museum in the Normannenstraße is impressive and very much worth a visit. And then, equally unmissable, the so-called
Museum Island, with the wonderful treasure trove that is the Pergamon museum (and several other major/great museums).
That should do it.