Kassel

Kassel needs 1 day: the Bergpark Wilhelmshöhe, a hillside park with the Hercules monument at the top and Europe's largest artificial cascade system, activated on set dates in summer, is the main reason to visit. May-September is best, to coincide with the cascades. It's inexpensive by German standards. Its Bergpark is a UNESCO World Heritage Site, and every five years the city hosts documenta, one of the world's most important contemporary art exhibitions.