Whenever you see Mannheim or Ludwigshafen on an itinerary, you will most likely be visiting Heidelberg. Heidelberg is a beautiful city with castle ruins overlooking from the mountain. I quite enjoyed my tour of castle with our very knowledgable tour guide. After the tour we made our way down for more food tasting and exploration at the Christmas Markets.
Heidelberg is another city that has multiple markets and a good amount of modern shopping. There was even a Lindt Chocolate store that had flavors I had never heard of. Be ready to stock up!