Pfalzgrafenstein Castle as seen from the Kaub, Germany side of the Rhine. The castle sits on a small island. The castle functioned as a toll-collecting station. It worked together with Gutenfels Castle and the fortified town of Kaub along the river. They even had a chain across the river to prevent boats from going by without paying their toll. Uncooperative traders could be kept in the dungeon until a ransom was delivered. The dungeon was a wooden float in the well!