Originally Posted by Telfes
A drive down the Main River toward Koblenz is lovely. Great way to spend a Sunday if the weather is at all good.
I second that! But I'd suggest taking the train, that way you can spend your time gazing at the beautiful scenery! It's a very nice ride.
Heidelberg is very picturesque, as is Koblenz. You might also want to look at Baden-Baden -- a day at the spa is definitely worth the trip, and the Casino is just stunning.