The Grey Tower forms the south-east corner of the former Nassau circular wall. The Nassau ring wall originally consisted of five towers. Today, two towers remain: the Eimelsturm at the Nassau cemetery and the Graue Turm in Grabenstraße.
The Grey Tower was built around 1400 and served a cruel justice from 1600 -1659: tower punishment, interrogation and torture of witches and sorcerers before their execution on the Hexenkippel near the summit cross on the Hohe Lay. This is why the tower is also called the witches' tower. The condemned served their sentence in the ground room, which had no walls or doors. The "interrogation room" below, which could only be reached by an outside staircase, contained the torture chair of the Nassau executioner. The once roofless, crenellated defence slab was reached by the tower guard via an inner spiral staircase of the tower wall from the upper floor. The tent roof of the tower is modern.