Another couple options for day trips are the technical museums in Sinsheim and Speyer.

http://sinsheim.technik-museum.de/en

Sinsheim is about 1 1/2 to 2 hours from K-town, depending on the traffic and is easy to find off of the A6 near Heilbronn. Speyer is a great town right on the Rhine river with an enormous gothic cathedral that is a UNESCO site in addition to their own technical museum: http://speyer.technik-museum.de/en

Speyer is about 40km or so from Sinsheim if you wanted to do them both in one day. There are plenty of good restaurants and outdoor cafes near the cathedral in Speyer as well. If you are driving from K-town, be aware that they are doing bridge construction on the bridge crossing the Rhine river that you will most likely be using (A61) and there tend to be traffic jams there, although they do move slowly. Plan on either factoring that into your trip time or research and alternate route. My GPS did a good job of routing me around it last weekend, but it was a Sunday morning when traffic tends to be light anyway. If you do have the train ticket I mentioned upthread, you would not be able to use it to visit both sites, as Sinsheim is in the state of Baden-Wurrtemberg and would not be covered on the Rheinland-Pfalz ticket.