 It is also a Grade I listed building (first listed in 1985), and recognised as an internationally important structure.It has been described as "perhaps the finest medieval landmark of the Peak District", and architectural historian Nikolaus Pevsner remarked that it is "By far the most important castle in the county – in fact the only one of importance".Before Duffield Castle in the south of the county was destroyed in 1266 it had one of the largest keeps in England, though only the foundations survive.