2 days in Berlin. On the first day, I wanted to do the whole Germany in WWII thing, so I took a guided walking tour. We visited the Brandenburg Gate, the Memorial to the Murdered Jews of Europe (named so because the holocaust, while mostly persecution of Jews, also included other groups - and Berlin has memorials for each of them), the former HQ of the Nazi Air Force, and several other sites. I really enjoyed the tour because I learned a lot more from the narrative than if I had just tried myself.
After the tour, I went to Museum Island, home to 5 different museums in central Berlin. I saw a few highlights - the Alter of Pergamon, the bust of Nefertiti, and the huge Ishtar gate from ancient Babylon. Really cool and really old stuff.
I tried to find a good, authentic German beer, and thought I had, but the bottle I had picked up ended up being some kind of dark, sugar-free bitter soda..
The next try, I actually ordered from a bar. I got a heffeweizen which is a German-style wheat beer. It was much better.
On day 2, I was a little hesitant to go to the highly recommended German History Museum due to hitting up a lot of museums the day before, but I'm really glad I did. It did a great job tracing German history (and really, European history in general) from about 100 AD to 1994. For obvious reasons, they devoted the entire first floor to 1919-1994. The format included an audio clip for each main period with accompanying objects to tell the story.
Then it was off to the Rhine Valley for our river cruise and castle exploration the next day.