The castle stands within what appears to be a bawn, a defensive enclosure typical of Irish fortifications from the plantation period. This rectangular earthwork measures approximately 64 metres from northwest to southeast and at least 40 metres from northeast to southwest, though time has obscured some of its original boundaries.

The surviving remnants of the bawn’s defences are most visible along the southwest and northeast sides, where an earthen bank still rises about 2 metres high and spans roughly 2 metres in width. These banks, now crowned with hedgerows, would have originally formed part of a complete defensive perimeter around the castle. Such bawns were essential features of Irish tower houses and castles, providing a secure area where livestock could be protected during raids and where the castle’s supporting structures, such as stables and stores, would have stood.

Archaeological surveys conducted by Michael Moore and documented in 2013 have helped piece together the layout of this defensive complex. Whilst much of the original fortification has been lost to centuries of agricultural use and natural erosion, the surviving earthworks offer valuable insights into how Anglo-Norman and later settlers organised their defensive settlements in medieval Ireland. The combination of castle and bawn at Cullenstown represents a common pattern of fortification that dotted the Irish landscape from the 15th through 17th centuries, when such defences were vital for survival in contested territories.