This Tudor castle, built in the 16th century, was designed by Sir Richard Lee in order to protect warships that anchored in the River Medway. Being of a military naval capacity, it is not surprising that the plan of Upnor Castle does not conform to traditional castle ideals.
Upnor Castle stands on the banks of the Medway and comprises a triangular water bastion, fronting a rectangular structure that housed the castle's living quarters. At either end of the castle wall, facing the Medway, are the North and South Towers.
The landward gatehouse and moat were added towards the end of the 16th century. At the same time the towers and walls were altered,and the timber palisade was constructed at the front of the water bastion. Most of Sir Richard Lee's work lies in the main building directly behind the bastion, with the original Tudor openings onto the riverfront being easily identified by their typical four-centred heads.
With the later addition of the moat, gunports from the lower parts of the two towers and the gatehouse were inserted for further protection. Although dating from the later building of the 16th century, the gatehouse was altered during the 17th century and this can be seen in the change of brickwork part way up the walls. Once through the gateway, a wide entrance passage leads into Upnor Castle, where foundations of various buildings can be made out.
During the 17th century the importance of Upnor Castle declined, and it was subsequently converted from service as a military fortress into use as a naval 'magazine'. This functional change meant that many alterations had to be made to the existing buildings, including removal of gun platforms, heightening of the North and South Towers, and further modifications to the main building. Upnor Castle retained its naval connections, serving as a magazine until the 19th century, and still boasts a remarkable state of preservation when looked upon from any angle, but is particularly impressive when viewed from the Medway.