It was built around 1100 by a Norman baron on a cliff that overlooked the above the River Nidd in Knaresborough, North Yorkshire. In the 1170s Hugh de Moreville and his followers took refuge there after assassinating Thomas Beckett.
It was regarded as an important northern fortress by King John and he spent £1290 on improvements to the castle. The castle was later rebuilt between 1301-1307 by Edward I and later completed by Edward II. John of Gaunt acquired the castle in 1372, adding it to the vast holdings of the Duchy of Lancaster.
During the Civil War, Parliamentarian troops took the castle in 1644. It was then largely destroyed in 1648 (slighted) because of an order from Parliament to dismantle all Royalist castles. This is why many town centre buildings are built of 'castle stone'
The remains are open to the public and there is a charge for entry to the interior remains. The grounds are used as a public leisure space, with a bowling green and putting green open during summer. It is also used as a performing space, with bands playing most afternoons through the summer.
The castle, now much ruined, comprised two walled baileys set one behind the other, with the outer bailey on the town side and the inner bailey on the cliff side. Solid towers lined the sides and 2 of these, still visible today, formed the main gate. At the junction between the inner and outer baileys, on the north side of the castle stood a tall five-sided keep, the eastern parts of which has been pulled down.