We are flying into Frankfurt because the fare is the best we can get. The next day we plan on flying from Franfurt-Hahn to Italy on Ryanair.

What is there to do for a day around Frankfurt? I've been to Frankfurt so I don't need to do that again. I'm most interested in an interesting small town in the area.

Hi athorp-

I don't know what your definition of "small town" is, but a few places come to mind. In parentheses are train travel time from Frankfurt.
Mainz (30mins)
Heidelberg (1hr)
Bonn (2hrs)
Cologne (1hr)

Depending how early you get into Frankfurt, you can even take the train to Koblenz (1.5hrs) and then board a boat and cruise Rhine river.

Since you'll be going to Hahn airport, might as well see something up that way.
Meander up the Rhine...Koblenz, Bacharach, St. Goar
Or check out the Mosel.....the town of Cochem (and the famous castle Burg Eltz).

The last couple of times I had a day to kill in Frankfurt before the real trip began, I took a train to Cologne and back through the Rhineland, stopping along the way in Bonn, Mainz and Koblenz. Wish I'd had time to tour some of the old castles (Burg Eltz and (?sp) von Katzenalenbogen). Another time, took a day trip to Heidelberg which was nice. Other possibilities as daytrips are Wurzburg and Marburg.

I mispelled the name von Katzenellenbogen. That name has more than a thousand years of history behind it. Ought to at least get it right.