Heidelberg

Heidelberg needs a day: the ruined castle overlooking the city and the old town by the Neckar river can be fully explored in a few hours. May-September brings the best weather. It's cheaper than Germany's major cities, though somewhat pricier than other university towns in the country. It's home to Germany's oldest university (founded in 1386), and its ruined castle, never rebuilt after several wartime destructions, is considered one of the most romantic examples of historic ruins in all of Europe.