Built by the O’Malley clan, who dominated much of the Mayo coastline during this period, the castle served as both a defensive stronghold and a symbol of their local authority. The structure follows the typical design of Irish tower houses of its era: a rectangular stone tower rising four storeys, with thick walls tapering as they ascend, narrow windows on the lower levels, and slightly larger openings above where the family quarters would have been located.

The castle’s strategic position near Lough Carra would have given the O’Malleys control over local waterways and trade routes, whilst providing a defensive advantage against rival clans. Like many tower houses built during this turbulent period of Irish history, Moyhenna was designed to withstand siege; its murder hole above the entrance, spiral staircase ascending clockwise to favour right-handed defenders, and bartizans projecting from the corners all speak to an age when local warfare was commonplace. The ground floor, with its vaulted stone ceiling, would have stored provisions and possibly housed livestock during raids, whilst the upper floors contained the main hall and private chambers, heated by large fireplaces whose chimneys are still visible in the remaining walls.

Today, Moyhenna Castle remains privately owned but stands as a roofless ruin, its walls largely intact but slowly surrendering to ivy and weather. The corbels that once supported wooden floors are still visible, jutting from the interior walls like stone brackets, whilst the remains of window seats and a garderobe (medieval toilet) offer glimpses into daily life five centuries ago. Though it lacks the grandeur of larger Irish castles, Moyhenna represents the hundreds of similar tower houses that once dotted the Irish landscape; functional fortified homes that sheltered Gaelic and Old English families through centuries of conflict, conquest, and change.