If you're staying in Munich you can visit the Nuremberg christmas market. With German rail, it is just a one hour ride from Munich.

Also still reachable in an acceptable timeframe (2 hours by train from Munich) is Bamberg, which is one of the few towns in Germany that wasn't destroyed during the 2nd world war. Its old city quarters are a UNESCO world heritage and definitely worth visiting. The beer there is also great (the small town (70K inhabitants) still has 11 local breweries).