The main structure is a rectangular hall that rises two storeys, though time has taken its toll on what was once likely an impressive defensive building. A tower once projected from the south side, with remnants still visible in the southwest corner, whilst a later addition extends from the northwest angle. The eastern end appears to have the remains of a bawn wall, which would have enclosed a courtyard area typical of Irish tower houses and castles.

Historical records place this castle firmly in the landscape of 17th century Ireland. The Down Survey maps of 1655 to 1656 clearly mark a castle at this location, suggesting it was still a notable structure in the aftermath of the Cromwellian conquest. However, by the time the Ordnance Survey arrived in the 1830s, local memory of the site had already faded. Their letters note that whilst old walls remained in Garrison townland and were thought to be fortress ruins, the local people had no knowledge of the castle’s history.

Today, these ruins stand as one of many forgotten strongholds scattered across the Irish countryside. Whether it served as a residence for a local lord, a military outpost, or both, the castle at Garrison was clearly built to command its surroundings from its elevated position. The combination of the hall structure, defensive tower, and possible bawn wall suggests this was once a substantial fortification, even if its specific story has been lost to time.