The site comprises a tower house and bawn wall, approximately 38 metres north to south and 50 metres east to west, that has undergone significant transformations since its earliest recorded mention in 1285. The defensive structures include towers at the southwest and southeast corners of the bawn, each roughly six metres square, with the distinctive Irish medieval feature of third storey bartizans corbelled out from the outermost corners. While the southeast tower remains complete as part of later farmhouse additions, only the stair turret and corbel supports survive from the upper portions of the southwest tower, along with remnants of a round staircase tower pierced with arrow slits that once rose three floors.

The castle’s documented history reveals a complex pattern of ownership and development. The 1654-56 Civil Survey recorded Edmund Fanning, an ‘Irish Papist’, as possessing one plowland with the castle, bawn, thatched house and orchard. By the 18th century, portions of the bawn wall had been demolished to accommodate a new house that faced the old courtyard with an impressive façade and bow fronted entrance, though nothing of this structure survives today. The Ordnance Survey map of 1840 shows the property accessed via a road from the east, marked by a gate lodge that still stands, with an old deer park located 780 metres to the east.

The current incarnation of Fanningstown Castle dates largely from around 1810, when substantial nineteenth century additions were made by P. Nagle of Cork. The complex now consists of a crenellated three storey block with various extensions, incorporating earlier medieval fabric into its interior. The limestone walls feature machicolations at the roofline and a garderobe like projection with blind cross loops on the south elevation. Adjacent to the bawn lies an extensive walled orchard with a round headed carriage arch featuring red brick voussoirs, possibly dating from the seventeenth century or earlier. This remarkable palimpsest of Irish castellated architecture, with its double battlements typical of medieval Irish fortifications, has recently been converted into four star self catering accommodation, ensuring its preservation for future generations whilst maintaining its historic character.