Heidelberg Free Time: Must do's in Heidelberg

Hotels:  NH Hirschberg Heidelberg (Main Group), NH Heidelberg (City) (Satellite Group)

http://www.rearviewmirror.tv/top-4-things-to-do-in-heidelberg/

We are going to visit the Heidelberg Castle as part of the tour.  We will have Friday night, Saturday 12-4 and after dinner for seeing the sites of the city.  

Maybe tour Heidelberg by bicycle?  The cost is 18 E per day.  Rent bikes by the Old Bridge.   Open Saturday 10- 6.
http://www.fahrradverleih-heidelberg.de/englische_seiten/prices_engl_fvhd.html