Heidelberg

What are your "sight"? You can definitely see the old town and take a tour through the castle - and go to the philosophers' path in one day! Heidelberg also has got a great (and young) night life. If you're into that you might want to consider an overnight's stay. Also if you want to take a Neckar river cruise e.g. to Dilsberg you'd need a second day. Dilsberg is a real medieval town just like Rothenburg - but not for the touists, for real people. In Google enter DILSBERG and then hit IMAGES.

Thanks Andreas We wanted to see the castle for sure. We will be taking a cruise in Cochem so maybe the old town and the castle would be okay for a day.

Definitely can be done in a day, the Altstadt is not that big. I will completely agree with Andreas that you need to take a walk up the Philosophenweg across the river. The views of the Altstadt are phenomenal. There's also a really cool old sketching up there of what Heidelberg looked like in the early 1600's, before the castle was destroyed.

Thanks again Rik Had originally booked 2 nights but have to back everything up in order to catch a cruise in Venice on time.

You can see most of the Altstadt and Schloss in about half a day. There's a lot of interesting stuff around Heidelberg that would, of course, take longer to explore. Worth seeing are Schloss Schwetzingen, the Heidelberg Thingstätte (an outdoor ampitheater from the Nazi era, located above the Philospher's Walk), the ruins of St. Michael's Abbey, and various towns and castles along the Neckar river valley (including the walled town of Dilsberg, mentioned by Andreas). Some are easy to reach via public transportation, some you need a car.