Pfalzgrafenstein is a historic castle located on an island in the Rhine River near Kaub, Germany. Built in the 14th century, it served as a toll station for river traffic, allowing the Electorate of the Palatinate to collect fees from passing ships. The castle's strategic position made it an important fortification during the Middle Ages. The castle features a distinctive round tower and thick stone walls, which have been well-preserved over the centuries. Today, Pfalzgrafenstein is a popular tourist attraction, offering visitors a glimpse into medieval architecture and the history of the Rhine Valley.