Not far from Speyer or Mannheim, on the way to Heidelberg, is the city of Schwetzingen.
There is a summer residence built for the electors of the Palatinate in the 18th century. The palace with the rococo-style theater has been partially preserved, but the main attraction, which claimed to be included in the UNESCO list, is the palace park, modeled after Versailles. In my opinion, UNESCO is maybe a little too much for them, but the park is really picturesque.