Welcome to Flyertalk. Your post will probably be moved to the Germany forum, where the FRA experts hang out. In the meantime there are a couple of threads (linked below) that might be helpful. The consensus seems to be you will have time for a quick trip to downtown Frankfurt, but a better option might be to go the other direction to Mainz:
6 Hours at FRA
Suggestions for an 8 hour layover in FRA?
Last edited by scoow; Jan 4, 2009 at 6:35 pm