The keep is the oldest preserved building on the castle hill. It was erected on its southern slope probably in the second half of the 13th century as a defensive and residential tower. It was part of a wooden castellan stronghold and was the only brick building at that time. The keep strengthened the location of the medieval complex, as it strengthened and secured access to the castellan’s seat. It performed primarily military functions, but also served as a refuge in the event of an emergency.
Its lower part was made of stone, and the upper part – of bricks. It has three above-ground and one underground storey, all of them with domed vaults. Inside, one can find a spiral staircase, and the walls are up to 3.5 meters thick. The Romanesque character of the building is evidenced, among others, by the Slavic arrangement of bricks, the shape of window openings and masks characteristic for the 12th and 13th centuries, as well as graffiti. One can also find the bifora window on the third floor interesting.
Since the 14th century, the keep served as a prison, where both the nobility who delayed the payment of debts and criminals, whose days were numbered, were kept. During architectural research, engraved inscriptions were discovered on five bricks on the first floor. They were left by prisoners held here at the beginning of the 17th century. The existence of a prison in the Lublin keep is confirmed by an entry from the inventory of the Lublin castle from 1564, as well as information from the Diariusz Lubelskiego Sejmu Unii (Lublin Union Sejm Diary): 1569.
In the 19th century, during the construction of the building intended for a prison, the keep was placed within its walls. The Neo-Gothic battlement at the top of it comes from this period.
During the Nazi occupation, in 1939–1944, it housed one of the toughest wards of the prison, known as Baszta I, II, III. In 1944–1954 a communist prison functioned here. Currently, the inside of the keep houses an exhibition devoted to the prison at the Lublin castle from the Middle Ages to 1954.
In 2012, the observation deck at the top of the keep was opened for visitors, from which one can admire the panorama of Lublin.