Potsdam
Potsdam, which was the summer residence of Frederick II, is now an elegant residential district, just 30 minutes away from the German capital on the S-Bahn. This glorious city has several parks, palaces and palatial mansions and other things to see. Here's my advice: leave at least a day to visit the city. In good weather, it's a good idea to visit the city on foot and walk around the gardens. On Mondays, entries to the palaces aren't allowed, but the gardens and parks are deserted.