That's not too bad. I've also looked into going to Wittenberg and it's only 40 min. each way by train. Too much to do in Germany for just one day with our German background. I really wish we had overnight there instead of in St. Petersberg.
This is what was done for us (modified set tour):
Agreed itinerary: Berlin Classical Tour and Sachsenhausen Memorial Museum
Norwegian Jewel
Tour program W.-Berlin-W. with 3 hours in Berlin and a private tour to Sachsenhausen
08.00 am Pick up at the ship in Warnemuende
11.00 am Arrival in Berlin, meeting your guide. A quick look at Charlottenburg palace and a short walk in the gardens
11.00 am -1.00 pm City sightseeing tour (with the group) covering the most interesting and important historical sights of
the Eastern part of Berlin: Checkpoint Charlie, the Berlin Wall, Brandenburg Gate, Book-burning memorial, the sight of
Hitlers bunker, TV tower, the City Hall, Berlin Cathedral, the Reichstag, the Holocaust memorial (a visit to the underground
documentation center is optional)
1.00-1.30 pm Snack in the coffee shop at Check point Charlie (optional)
1.30-2.10 pm Meet your private guide and driver. Drive to Sachsenhausen
2.15-4.45pm Excursion in Sachsenhausen memorial museum
05.00 pm Meet with the group. Departure to Warnemuende
08.00 pm Arrival in Warnemuende/Return to the ship
The tour includes the following services:
Transfer Warnemuende-Berlin-Warnemuende by an A/C vehicle
City sight-seeing tour in Berlin (with a group)
Private vehicle for 3 hours in Berlin/Sachsenhausen