We went to Heidelburg last year as part of a visit to another place(Lake Constance a rail journey away). I wouldn,t especially rate Heidelburg against other places in southern Germany. It was basically a long, no very long, if old shopping street with a cathederal at the end of it with market stalls sticking on to the side of it.There is a castle on the cliff-top above which is striking and looks great when lit up at night.There is a river and main bridge neither of which are really noteworthy. The hotel we stayed in was'nt great but that was our fault for not researching the place beforehand.We went in summer time and I would imagine the place might be better if there is a Christmas Market on though there are plenty of really good Christmas markets in other towns. The food was ok, there was a traditional German food tavern near the bridge which was good and had a good atmosphere. I don't really want to put you off and I'm sure others may have a different and better opinion.