I have a one day transit in Frankfurt next month. Never been to Germany before and have no clue. Would like to get some advice on what to do. Should I stay in Frankfurt and do a city tour? Or should I head over to Mainz where I can stay at the Hyatt Regency? What's there to do in Mainz?

Also, from reading this thread, it seems like travel between FRA airport and HR Mainz is pretty simple. I understand that I should take the train to Mainz Sud. What's the train station at Frankfurt? Is it right next to the airport?

Thanks for the assistance.