Some of the best German memories I have are from the day I spent traveling through the Upper Middle Rhine Valley by boat between St Goar and Bacharach. The Rhine River cuts a gorge through this section of western Germany, and the steep hillsides covered with terraced vineyards were spectacular in autumn. The Lorelei rock near St Goar was pretty impressive as viewed from the river, even with its siren mythology that speaks of rivermen becoming distracted and crashing against the rock. All along the river were fortresses that highlighted the importance of river trade throughout the centuries, including Rheinfels Castle, Katz Castle, and Pfalzgrafstein Castle, which was built on an island in the river and served as a toll station for passing vessels. This section of the Rhine is incredibly memorable, and, like Klaus and Gatis, I am surprised it took until 2002 for this German cultural treasure to be inscribed as a World Heritage Site. I would highly recommend a trip along the Rhine to anyone traveling through Germany.
Logistics: The Upper Middle Rhine Valley can be seen by train, automobile, or foot, but I highly recommend traveling the river by boat.