The keep standing c 33m high, with four storeys still largely intact. It is built of ashlar from Barnack, near Peterborough, and is square in plan, with tall rectangular turrets at opposite corners projecting above the rooftop.
There was originally a forebuilding standing in front of the entrance, with a set of stairs leading to a first-floor entrance. The forebuilding is now mostly ruined, but the Norman entrance door, with its portcullis groove, is still used.
See also: Historic England: Hedingham Castle