Berlin is truly amazing. And it is completely different each time you go ( things are changing so fast ) so even if you've "done" it already, you really haven't. See what's left of the Wall and the Death Strip ( many remnants left ) and the earlier Third Reich and First Reich historical architecture. And so many museums! I like the Technology museum in the old bombed out Potsdamer Bahnhof - lots of old trains and whatnot. A really fascinating side trip is to Auschwitz and Krakow in neighboring Poland. It can be done by train over a weekend. No visa needed for Americans. Also less known is the Volkswagen museum in nearby Wolfsburg (if you like old bugs) and the East German museum in Eisenhuettenstadt (sp?) a couple of hours away (if you like old Trabis and other extinct everyday items). Enjoy yourself!