Restormel is the best surviving example in the UK of a circular castle - 125 feet in diameter, mostly built in the 13th century, when, for a short time, such designs were favoured. The castle sits on a narrow spur overlooking an ancient crossing point on the River Fowey, 1 mile north of Lostwithiel and 2 miles from the start of the broad river estuary, so most likely the southernmost ford along the river.
The castle probably began as a traditional motte and bailey fortification soon after the Norman conquest, and was converted to stone by local Lord Robert de Cardinham, though was in use for only around 100 years; apart from sporadic occupations, the structure has been mostly abandoned since the early 14th century.
The ruins are substantial, and photogenic - the castle is surrounded by woods and grassland, and still has commanding views of the valley and the surrounding hilly land. This site is managed by English Heritage, and fees are charged for entry.
The early history of Restormel Castle is somewhat uncertain, but it was likely constructed by Baldwin FitzTurstin, local sheriff, son of one of the companions of William the Conqueror. It consisted of a ring ditch surrounding a circular mound topped by the timber fortification; four pits, cut into the slate bedrock, are likely to date from this period. Partial rebuilding in stone, starting with the gatehouse, was carried out by the Cardinham family at the start of the 13th century, and they resided here for several decades until it passed to the Earls of Cornwall - it was Edmund, the second earl, who further enhanced the buildings, completing the structure seen today. The castle at this time was surrounded by the largest deer hunting park in Cornwall. The walls were made of slate, most likely excavated from a quarry just to the north, still evident today.
Restormel Castle was transferred to the crown after Edmund died in 1299 without heirs, and was never again regularly occupied. Edward the Black Prince (son of Edward III) stayed here on occasions, and carried out some repairs, then the place was briefly in use during the Civil War, but otherwise the castle has lain empty for centuries, gradually decaying. Around the Civil War, the local landowner was resident in Trinity House, now known as Restormel Manor, a mansion right beside the river a short distance east, and later occupants of the manor treated the castle as a romantic ruin, planting trees all around the site to enhance its picturesque setting. The crumbling, ivy clad structure was repaired and partially reconstructed in the 1920s, after transfer to the Office of Works.
Restormel Castle is approached by a short side road off Restormel Road, on the north side of Lostwithiel. From the parking place, a path passes the English Heritage fee booth, flanked by a group of rhododendron trees, and emerges to an open, grassy ridge, with the castle at the far end. The grounds are a popular place for picnics, and a small cafe operates most of the year. Entrance to the castle is via a bridge over the ditch - originally a drawbridge, operated from the two-storey gatehouse just beyond. A passageway leads into the circular courtyard, ringed by rooms all around - on the ground floor were cellars and guard rooms, plus the kitchen and servery, while above was the wardrobe, chapel, two halls and several service rooms, and above this, a wall walk, encircling the whole building. One interruption to the perfectly circular outline is on the north side, where the square chapel of St Mary projects outwards. The actual chapel is on the upper floor, probably on a solid base. The chapel contains one modification from the Civil War, filling in of the frames of the main external window by masonry, in order to support the weight of cannons that were installed on its roof.