A lot of people just do day cruises on the Rhine. Bingen and Koblenz are the scenic parts of the Rhine River, to be sure. But if you're going alone, a cruise alone the river can be an excellent way to get a feel for some of Europe's best attractions.
You can stay in the cities and not see the countryside, or you can take the train all over the map... and have the countryside blur by you at frightening speeds. I like the boat because it is slow, leisurely, and actually feels like a vacation.
For a 1.5 week trip (which I think is about the max most of us can do on vacation), here's what I would recommend for a Rhine River Cruise:
You can get all the way from Amsterdam to Colmar in nine days, at a relaxed pace, seeing a ton of quaint locations along the way.
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