The medieval city of Heidelberg is about an hour and 15 minute train ride from Frankfurt. It's located on the Neckar River and the Altstadt (Old Town) has nice views of the Heidelberg Castle and the scenic Old Bridge.
On the far side of the river there are paths going up the hill with the best views of the Old Town, Castle, and Bridge.
This was our last day in Germany and the end of the vacation. Tomorrow it's time to fly home.