Kasteln Castle (German: Schloss Kasteln) is a castle in the municipality of Oberflachs in Canton Aargau, Switzerland. It is located west of the village on a rocky outcrop, surrounded by vineyards and woods. Today, it serves as a boarding school for students with behavioral problems. The immediately adjacent castle Ruchenstein was demolished in 1643, when the small fort was rebuilt into a Schloss Kasteln.