The Pfalzgrafenstein Castle is the signature castle in the Rhine River of Germany. The keep of this island castle, a pentagonal tower with its point upstream, was erected 1326 to 1327 by King Ludwig the Bavarian. Around the tower, a defensive hexagonal wall was built between 1338 to 1340. Later additions were made in 1607 and 1755, consisting of corner turrets, the gun bastion pointing upstream, and the characteristic baroque tower cap. The castle would string chains across the Rhine blocking passage of shipping until a toll was paid.
This portion of the Rhine River Valley is a UNESCO World Heritage Site containing castles about every mile of the river. The best way to see the castles is to take a cruise up the river. There are also roads paralleling the river that can be driven on both sides.
Get off the road and up into some of the castles. Some of them have been converted into hotels or inns, some are ruins and some are museums. The views down into the river are also spectacular.
Even in the winter you can visit many of the castles with the added bonus that you might find yourself completely alone as we did on a subsequent trip. Well worth the trudge up the ice path.