Home to the oldest university in Germany, Heidelberg was hit hard during 17th-century wars and rebuilt in the 18th century with baroque buildings. For a pleasant walk, stroll through the historic city center's Gothic streets. Be sure to take in Heidelberg Castle, the symbolic heart of the city; Alte Brucke, a beautiful 18th-century bridge; and the Student Jail. Built as long ago as the 16th century, it was used to keep mischievous students off the streets for three days to a month at a time. And they say Penn State is the number-one party school!