Dunstanburgh is a superbly located castle on an outcrop of the Whin Sill.
The Castle is a scheduled monument and Grade I listed. Link
Wikipedia Link gives more information on the castle and its history.
NU2521 : Great Keep - Dunstanburgh Castle The Great Gatehouse of Dunstanburgh, begun in 1313 by Thomas of Lancaster, had its passageway walled up in 1380 when John of Gaunt built his gatehouse to the northwest. The great gatehouse with its distinctive twin D-shape towers, was then used as a keep.