The Rhine Valley is THE classic German, and maybe even European, landscape, and should have been the first German site on the list, as suggested below. Well, in the early years UNESCO didn't accept cultural landscapes, but they made good in 2002. The site includes the most well-known stretch of the river between Koblenz (where the Moselle meets the Rhine at the Deutsches Eck) and Bingen. In between, there are countless small towns such as St. Goar and St. Goarshausen, connected by a ferry offering you a nice view of the vineyards on the shore. Close by is the famous Loreley rock, which is actually quite unremarkable today, because much of it was blown off in the early 20th century to make the passage easier for ships. I would have loved to see a castle or two, but it was raining too heavily, and the Rhine was almost at flood-level. It is obvious that the region's heyday as a tourist destination is over (I have never seen two more derelict train stations than in the two towns mentioned above), but it is still a very nice region that deserves a longer visit than most people give it.