We are registered for the Best of Germany tour in May 2023. We plan to spend several additional days in Berlin after the tour. We definitely plan to go to Potsdam one day. What additional day trips do you recommmend? Thank you.
Sachsenhausen
Leipzig
Not quite as far as Leipzig is UNESCO WHS Gartenreich Dessau-Worlitz, if you like that sort of thing, as we do. Many outdoor lunch options nearby in season. Another closer-in trip is the Gründerzeitmuseum in Mahlsdorf. It's a very long walk, or a cab ride from a Berlin SB train stop, very easy to get to. It's related to the Pulitzer Prize winning play "I am My Own Wife", but in that sense is a also a Nazi-era and Stasi-era stop. Limited English tours by appointment only.
How far from Berlin do you want to go? Presumably, within 1-2 hours. Lots of choices here, depending on your interests aside from Potsdam.
I would suggest Leipzig, Lutherstadt-Wittenberg, Rheinsberg, and Halle, as suggested above. For a specific WW2 place, then Seelow, if the distance is not a major concern. I did day trips to these places from Berlin, also the length of time depends of the train, the ICE or a regional train.