Standing in ruins on top of the cliffs in the north-west corner of Jersey, Grosnez Castle is something of a mystery. Nobody knows when it was built, or exactly why, nor when it was ruined. It could not have been intended to keep invaders out of the island, but perhaps it was a safe refuge for the population after they had arrived.
The walls were built from granite and are thickest on the landward side, because on the three other sides it is protected by steep cliffs some 60 metres high. The perimeter wall was about 250 metres long and enclosed an area roughly circular in shape.
The gatehouse, which is substantially all that remains, was protected by the drawbridge and portcullis and would have been very difficult to capture.