Originally Posted by
LondonElite
That's a bit harsh I think, but there aren't a huge amount of touristy things to do around Frankfurt.
The Rhone valley would be quite a trek from Frankfurt - a few hundred kilometers southwest. I think you mean the Rhine valley (Rhein in German). The city is on the Main river, which flows into the Rhine, and there are some beautiful vineyards around there.
That is why I recommended Mainz. Heidelberg would also be a close, good choice. Small enough to cover everything in a day.
If you search this forum, there are some great ideas for Munich.
Also, what I did was use a combination of google maps and Bahn.de to do some scouting. Figured out where I would want to go on google, then plug in the stations on bahn.de.