Hammerstein Castle (Burg Hammerstein) is the ruin of a 10th-century mountain castle in Rhineland-Palatinate, Germany, the oldest in this entire Middle Rhine Valley. The ruin of one of its watchtowers still overlooks the Rhine at an altitude of 195 m, near the village of Hammerstein.[1] The Rheinsteig hiking trail passes close to the ruins which can be reached via a small path.[2]