If you are going to Frankfurt for a weekend, there are many things you can see and do in this city on the river Main. Here is the list of attractions and activities I would recommend for a perfect weekend in Frankfurt.
Tag: Germany

Scenic Middle Rhine cruise in Germany
Example itinerary from Frankfurt to Koblenz that includes scenic Middle Rhine cruise, walk in Boppard and half a day in Koblenz.

What to see in Cologne in a day or two
List of things to do and see in Cologne if you have a day or two.