Berlin: Nights 1-4, plenty of WW II there. Spend an extra night if you want to visit Sanssouci Palace in Potsdam? (Train from Berlin at 2-3 pm on your final Berlin day and arrive between 7 pm and 9 pm in...)
Rhine Valley: Nights 5-6, castles castles castles. Do a Rhine castle cruise past dozens of castles; tour Rheinfels Castle in St. Goar and Marksburg Castle in Braubach, visit Bacharach and another old-world town or two. Overnight in St. Goar, probably the most convenient base for train outings and where 3 castles are visible from town - this is the most scenic part of the river. Stay at least half a day here on Day 7 as well. Leave the area at around 3-4 pm and arrive about 3-4 hours later in...
??? I guess you could just go to Munich for the rest of your time if you are lacking alternatives, but alternatives there are, and Munich would be a second mega-city that like Berlin was bombed out and rebuilt. So I suggest you look into other Bavarian options - that are on your way to Munich - like...
Nuremberg: Nights 7-9, varied options in town and a base for easy day trips by train. Nuremberg was also bombed heavily and rebuilt but they sure rebuilt it nicely. Nice old town zone WW II stuff and much more, including some nice pubs. A day trip on Day 8 or Day 9 would be possible - take your pick of several Bavarian towns - Bamberg or Rothenburg (tourist central) or Iphofen or Bad Windsheim are all different sorts of experiences. Pick what suits you. On Day 10 see some more of Nuremberg before you head to MUC airport for your final night.
Bavaria is huge - like a country unto itself - so there's no way you can experience Bavaria in just a few nights. But you can get some variety for sure if you go with Nuremberg + an outing or two.
