The Romanesque defensive tower, also known as 'donjon', is the oldest building on the castle hill. The tower was built of stone and brick around the middle of the 13th century in the form of a cylindrical, homogeneous building showing the features of the late Romanesque style. The building was erected in a typical way for the 13th-century fortress - inside the defensive ring, as the main center of fortifications. The tower is around 20-meter high and the thickness of its walls at the basement level comes to 4 meters. The highest part of the tower is lit by a biforium - a type of window characteristic of Romanesque architecture divided into two parts by a stone column. The top of the tower features a viewing terrace with a beautiful view onto the Old Town and the surrounding area.
Along with the Castle Chapel, it was the only part survived after destruction of the castle during the wars in the 17th century. From 1826, the tower and the castle served as a prison. From 1957, the exhibition halls of the Lublin Museum are located there.