Most all of the castles on the Rhine are on the banks of what they call the Romantic Rhine. The Upper Middle Rhine Valley as it is called is a UNESCO World Heritage Site. Going north from Rudesheim to Koblenz it's a stretch covering about 40 miles. Here the Rhine is in a valley with generally steep sides covered with woods and vineyards. The Lorelei, that place of legend, is not quite halfway up the Romantic Rhine. There are 12 castles and 2 toll stations before you get to the Lorelei and another 14 from there to Koblenz. Some are legitimate ruins, some are maintained as restaurants and hotels, some are museums and all are exciting and intimidating to river traffic in their day. Some were owned by royalty, some by the real robber barons, some by the church and some by nearby towns. Almost all collected a fee from merchant ships which allowed them to pass unmolested. Some were built to protect towns or churches from brigands.
You can follow the Romantic Rhine route with the castles photos from various angles at the website below. There you will find some short description of the castle, who founded it, when and sometimes a short history with some surprising things you might never have guessed.
http://www.loreley-info.com/eng/rhein-rhine/castles.php
We only have 10 different castles/fortresses and 1 toll station to show you now, so we are hoping for some additions from our fellow travelers.