Lancaster Castle in England, UK and its noteworthy neighbour, the priory church, crown the pinnacle of a hill overlooking the River Lune. Following the influx of the invading Normans, Lancaster became part of the vast estate granted to Roger de Poitou and the first castle is very likely to have been his base.

In 1265, the castle became the chief seat of the controlling lords who followed, together with Thomas, ring leader of the baronial opposition to Edward II; Henry, the foremost palatine duke; and john of Gaunt, who then married his way into the duchy. When John of Gaunt's son seized the throne as Henry IV in 1399, and the following union of the Duchy of Lancaster with the Crown, the castle fell into decline as a dwelling but remained the administrative center of the Duchy. It remained very much a working Castle, still serving as a courthouse and prison facility.

Late on in the 18th Century, the Castle was significantly modified to be used as a court and prison, during this period the medieval curtain wall and several of the towers were knocked down. The remaining towers enclose an area roughly corresponding with the medieval bailey, except on the north side where the prison juts out in a big arc. Furthermore, a series of assize buildings, notably the semi-circular Shire Hall, projects on the west.

Fortunately, a few significant pieces of the medieval castle have been preserved. The finest of these is John of Gaunt's Gate, which is one of the most majestic of medieval English gatehouses. It is a enormous and rather austere-looking block as befits the entrance to a prison.

There is a continuous parapet around the wall head and the well-proportioned gateway preserves its original portcullis. Semi-octagonal towers that carry inner turrets above parapet level flank it. The circular Hadrian Tower forms part of the Shire Hall complex. Today the castle is used as a class C prison so a sizeable section of it is not open for people to look around; however there is still a large piece of the building available for tours.