Germany 2017 - The Short Version - wesk8
The town of Kaub and Gutenfels Castle.  Together with Pfalzgrafenstein, they would have made a strong fortification to collect tolls from passing ships.  Note that this side of the river was the only navigable side.  The other side had steep rapids and essentially prevented travel on the left side of Pfalzgrafenstein, forcing ships into this narrow passageway.  Those rapids were removed in the 1800s and the other side is now the main passageway.

The town of Kaub and Gutenfels Castle. Together with Pfalzgrafenstein, they would have made a strong fortification to collect tolls from passing ships. Note that this side of the river was the only navigable side. The other side had steep rapids and essentially prevented travel on the left side of Pfalzgrafenstein, forcing ships into this narrow passageway. Those rapids were removed in the 1800s and the other side is now the main passageway.