If you are interested in wine areas, you should visit the Rheingau. It starts Hochheim and goes on the right side of the Rhine up to the city of Lorch. What you can do is to take a trip on a KD-Ship Köln-Düsseldorfer. They have larger ships going up and down the Rhine. Just go for example all the way up to Lorch and from there go back by train to Frankfurt. Alternatively do a trip to Kloster Eberbach Kloster Eberbach. The movie "In the name of the rose" with Sean Connery was filmed there. They sell also excellent wine (mainly Riesling). The monastery is part of the state winery of the state of Hessen.

In Berlin you can do guided underground tours through old WWII bunkers. http://www.berliner-unterwelten.de/en.html

From Munich Airport to Dachau is bit a way. You need to take the S-bahn into town and change there to Dachau. Best probably take the S1 to Laim and change there onto the S2 to Dachau. Or you go to main station and put your luggage in one of the lockers there.

Suggestions for Munich are the Deutsche Museum (it is a bit the like the Smithsonian), the Residenz (the place were the bavarian kings lived in Munich) with its treasury is very interesting, a stroll over the Viktualien market is a must, the 1972 summer olympics park is nice, a walk through English Garden is also a must, the typical tour starts at the Eisbach Welle (the place were all the surfers are, because the small river there has natural surf wave) towards the Chinese Tower beer garden. If you are into cars the BMW museum is very interesting.

Hope this gives you some inspiration.