I am planning a trip for this fall (late October) to Germany. I have been to Munich a few times before and do not plan to do Munich again. A friend currently lives in Frankfurt so I will spend at least a few days in Frankfurt - maybe more if I can use that as a base to do some side trips. Just trying to get suggestions for a possible itinerary. I'd like to be able to travel only by train/bus - I don't want to have to rent a car. I like to be very active and enjoy walking/hiking a lot. I love seeing historical sites and castles/fortresses and such. I think Berlin is probably a must-see, but not sure how many days to spend there.
Any suggestions would be greatly appreciated! And yes, I know late October is not the ideal time to go, but it is the only time I can take vacation from work.