Lahneck Castle is a medieval fortress located in the city of Lahnstein in Rhineland-Palatinate, Germany, south of Koblenz. The 13th-century castle stands on a steep rock salient above the confluence of the Lahn River with the Rhine, opposite Stolzenfels Castle, in the district of Oberlahnstein. Its symmetrical plan, an oblong rectangle, is typical of the later castles of the time of the Hohenstaufen. The pentagonal shape of the bergfried is rare for castle towers.