Defensive Tower of Chartoryski and fragment of the well are the remnants of the Surrounding Castle fortification, that during the medieval times strengthened the Upper Castle from South and West. The Surrounding Castle consisted of 8 towers, although half of them were wooden. Entrance to the territory was made using the bridge over the moat, that was filled with water (ran through the current Drahomanova st.). Within time, the fortifications were gradually getting dismantled and ruined, and the moats got filled up. Only one tower is preserved until today, named after Czartoryski princes, a famous noble family, that lived in Lutsk during XV-XVI centuries.
Under the tower, underground rooms can be found, that apparently were connected to the dungeons under the Cathedral.
Right now, the tower is under reconstruction and an opening of the modern museum with the use of 3D effects, holograms, where temporary thematic exhibitions will take place, is planned