The five-storey limestone structure, measuring roughly 9 by 11 metres, rises impressively from its surroundings, with farm buildings nearby and the medieval St. Johnstown church and graveyard just 110 metres to the northeast. Historical records from the Civil Survey of 1654-56 note that Robert St. John of St. Johnstown held the property in 1640, when it was described as ‘a Castle with a Bawne about it which is in repaire’, suggesting it still retained its defensive enclosure at that time.

The tower’s defensive features reveal the paranoia and ingenuity of its builders. Entry is through a pointed doorway on the west wall, protected by an elaborate system of murder holes, yett holes for securing gates, and a machicolation above with three gun loops. Once inside, visitors would have faced a quatrefoil shot hole directly opposite the entrance; an unusual defensive feature accessed from the ground floor chamber. The spiral staircase in the northwest corner contains its own built-in shot hole within the steps themselves, whilst throughout the building, gun loops flank most windows, creating overlapping fields of fire. Perhaps most chilling is the oubliette on the second floor; a windowless pit prison roughly 5 metres long and 2 metres high, accessed through a trapdoor that could be secured with a drawbar.

Despite its fortress-like qualities, the castle also served as a comfortable residence. Each floor contains a main chamber with increasingly sophisticated window designs as you ascend; from simple round and ogee-headed openings on the ground floor to elegant two-light windows on the upper levels. The second and fourth floors feature joggle-jointed fireplaces, whilst mural chambers throughout the building housed garderobes, storage spaces and additional defensive positions. Above the main structure, a caphouse tops the spiral stair, giving access to the wall-walk and two angle bartizans at the northeast and southwest corners. The presence of Robert St. John’s coat of arms above the entrance door, along with evidence of adjoining buildings visible in the south wall’s roof scars, suggests this was once the centrepiece of a larger complex befitting a gentleman of standing in Tudor Ireland.