a VirtualTourist member from Dallas
Do all the trains between Frankfurt-Mainz-Cologne follow the Rhine River? If not I would like to know the one(s) that does.
I'm not to familiar with this part of Germany, but I can say that not all rail routes follow the Rhine, a new high speed rail line was built inland. Take German Rail (Deutsches Bahn) from Frankfurt to Koln (Cologne) along the Rhine River and sit in the restaurant car all the way. You can see all Burgen (castles) and river traffic. I don't know the number of the route although.
Hope this was of some help ;)