Ralfkrippner mentioned already that you might go to Mainz or Wiesbaden. I am not so shure about Mainz, but I know the train/S-Bahn goes directly to Wiesbaden.
It it a very nice town: Wilhelmstrasse, Marktplatz/Altstadt (Old Town), Kurpark and Casino (Roulete, Baccara etc.; opens at 3:00PM).