We will be traveling from Offenburg to Garmisch-Partenkirchen the end of July and have an extra day to spend. We would like some advice, do we go straight to Garmisch-Partenkirchen or use a day and stay somewhere along the way? Do we make a reservation or take the chance and find something along the way?
Sigmaringen is a good intermediate stop between Offenburg and Bavaria. I've stopped there three times myself.
Another place would be Lindau.
Sigmaringen has a cool castle, but the rest of the town is mostly uninteresting. This area of southern Swabia features a decent, if not particularly large number of castles and preserved towns, but I found that for driving, the scenery overall is rather dull. At least until the Alps pop up on the horizon.
If flamboyant Rococo does it for you, check out the abbeys at Ochsenhausen and Ottobeuren. And if you're in that general area, check out the preserved, semi-walled Baroque city of Memmingen.