You specifically asked about concentration camps...I would highly recommend Dachau, basically where it all started and came to an end from what I understand. I was there last summer and it was quite powerful. It is just on the Northern edge of Munich.

I you are driving FRA to MUC, I would recommend going a bit less direct and pass along the Bodensee Lake in the South. Lots of neat old towns (we stayed a night in, I think Meersburg) and there is a well-done Zepplin museum in Frederichshafen.

Haven't been to Rothenburg, Würzburg but I thought Heidelberg was very cool.

Have fun!