Pfalzgrafenstein Castle is a toll castle on the Falkenau island, otherwise known as Pfalz Island in the River Rhine near Kaub, Germany. Known as "the Pfalz", this former stronghold is famous for its picturesque and unique setting. The keep of this island castle, a pentagonal tower with its point upstream, was erected between 1326 and 1327 by King Ludwig the Bavarian. Around the tower, a defensive hexagonal wall was built between 1338 and 1340. In 1477 Pfalzgrafenstein was passed as deposit to the Count of Katzenelnbogen.[1] 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 functioned as a toll-collecting station that was not to be ignored. It worked in concert with Gutenfels Castle and the fortified town of Kaub on the right side of the river. Due to a dangerous cataract on the river's left, about a kilometer upstream, every vessel would have to use the fairway nearer to the right bank, thus floating downstream between the mighty fortress on the vessel's left and the town and castle on its right. A chain across the river drawn between those two fortifications forced ships to submit, and uncooperative traders could be kept in the dungeon until a ransom was delivered. The dungeon was a wooden float in the well.