On Mon, 22 Sep 2014, Frank Hucklenbroich wrote:

My plan was to spend the first day there, then go to Nuremberg for
another day.

Places like Mainz, Wiesbaden, Darmstadt, Aschaffenburg, Limburg,
Wurzburg, Michelstadt are all within easy train reach. Some of them are
not utterly interesting but are fine for a few hour trip. The most
interesting are possibly Wurzburg and Mainz. A scenic possibility is
navigation on the Rhine from Mainz to Koblenz. Or some walk in the
hills ... the Odenwald is probably too south, but some Taunus place like
Bad Homburg should be reachable by S-Bahn.