Does anyone know of any car rentals in Boppard or Bacharach? Thinking just for the day to go out into the countryside. We are arriving by train.
There are none. These are small towns. You want a car you go to Koblenz or Mainz.
If you are staying in Boppard, you can get on any train (and any bus) within the entire VRM (Rhine/Mosel region that you see on the map below) and take a sightseeing ride at any time you want. The Guest Ticket that comes with your room covers you for free.
The Lahn and Mosel river valleys (see map) have their own train lines. Great scenery too - use the Mosel line to ride to Bullay and Traben-Trarbach, or up the Lahn to LImburg.
On the Rhine, there are railways on each river bank to around Remagen in the north, and to Oberwesel or Rüdesheim in the south.
The Mosel and the Rhine are commonly known as Germany's most scenic train rides.