We will be in Europe July 18-Aug 3. Plan to spend 5 days in London and surrounding. Normandy for a couple of days. Then we want to go to Cologne as a launch point for the Rhine? What is the best place-tour for seeing the Rhine, and maybe the Mosel (Rick highlights a 36 mile stretch which is the best part of the Rhine. How is this accessed?) The plan is to drive to Heidleberg, Rothenburg, Munich, Innsbruck, Salzburg (maybe Vienna if time permits) Then fly back to London for return trip.
Cologne is swell, but not a scenic boat area.
These may be helpful:
What is the best place-tour for seeing the Rhine
Not Cologne. Boppard (south of Koblenz) is a very nice old-world, riverfront town with lots of accommodations and dining choices and centrally located for the area's highlights. See map with towns and castles:
http://schnuggel-elsje.de/upload/Bilder/IMG_0131.JPG
https://www.youtube.com/watch?v=J2IjTma6VRY
Gedeonseck, just above Boppard - nice spot at top of chairlift ride (or drive up)
Boppard has a convenient ferry crossing if you wish to drive on the opposite river bank to Marksburg Castle in Braubach, or south to Rüdesheim.
The most scenic part (the part you probably want to cruise) is between Bingen and Boppard. This is actually about 26 miles altogether. The way to do the cruise if you're staying in Boppard is to simply take the train south to Bingen, then the cruise boat back to Boppard.
Here is the KD boat schedule.
http://www.kdrhine.com/rhineschedule.htm
Mosel is best explored by train, as there are a lot of locks along the way that really slows things down. You can get day passes for the area from the VRM, like 23 EUR for a group up to 5 traveling on regional trains and buses after 9 am week days, any time weekends. Covers Rhine down to Oberwesel and the Mosel to Bullay.