Maybe three days, staying downtown, my wife and I and three older teenage boys. They are obvioulsy interested in WWII, and german heritage. We are heading south from there (Munich - Salzburg - Interlaken). Suggestions on what to see? It will be our first 2-3 day leg of our trip.
You need at least two full days for all the main sights and attractions in the city of Berlin and a full day for the castles and other sights in Potsdam. From there it would then be a straight 8-10 hours drive down to Munich. You'd be passing Leipzig, Erfurt and Nuremberg which are also very much worthwhile but visiting them - at least briefly - would cost you at least one if not 1 1/2 more days...
My suggestions for Berlin would be to start a walking day from Potsdamer Platz - from there you can begin a walk starting with following the old route of the Berlin Wall. There are sections you can view there as well as bricks in the sidewalk and road showing the wall route. Walk along to the Jewish Memorial, then to the Brandenburg Gate, through the park to the Reichstag, through the Parliament buildings mall (Unter den Linden) to the Victory Tower (you can climb). If you purchase a multiple day rail pass this will include buses - you can hop on these too.
Check Point Charles although historic is unimpressive - but the historical walk with the billboards is awesome.
I would also recommend Kaiser-Welhelm Church - it was left standing as a reminder of the war - it is impressive - this is in the center of West Berlin at Breitcheidplatz.
Look for the Ampelmann in East Germany side (crosswalk men) - famous - there is also a store should you get hooked. http://www.ampelmann.de/
Thanks ... sounding great.
You can see a lot in Berlin in two days. The S- and U- bahn subway networks make it easy and quick to get around.
Jona's suggestions are great. For me, Kaiser Wilhelm church, the Reichstag and its views of the city, the remaining section of the wall with its murals, and the Soviet war memorial park were the most interesting and moving.
If you would prefer, we did a bike tour of Berlin. It took us throughout the area and showed us the main sights in about 4 hours. It was called Fat Tire Tours. They offer different types of tours. Check out the web site at:
http://www.fattirebiketoursberlin.com/