Just to give another region of Germany a chance ... why not visit North Rhine-Westphalia or Rhineland-Palatinate, which are easily acesssable by train (4h40 from Munich) and car.

Some nice places to visit are
- Cologne (my home town with nice sights, roman history, art galleries, food and many more), - Bonn (the former capital with a interesting background when you are interesed in the newer german history),
- Koblenz
- The Rhine Gorge with the Lorelei and some nicer villages along "Father Rhine",
- The Ahr valley (if you are interesed in wine and food, there are some nice high quality restaurants),
- Düsseldorf
- The Ruhr Metropolitan Region (the fifth largest urban area in Europe with a rich historical, cultural and industrial background)
...

Concerning the trip from Munich: Perhaps you might consider taking a night train from Munich to Cologne?

If you are interested or have any questions, don´t hestitate to contact me.