Local antiquarian Windele once suggested the castle guarded a ford across the river below. Though ivy masks much of the exterior walls today, the structure reveals fascinating defensive and domestic features typical of Irish tower houses. The entrance arrangement is particularly interesting, with ground and first-floor doorways positioned one above the other near the southern end of the western wall, allowing defenders to control access to the upper levels even if the ground floor was breached.

Inside, the castle’s chambers tell a story of medieval life and warfare. The ground floor chamber, once covered by a wicker-centred vault of which only the springings remain, measures 4.2 by 2.5 metres and features double-splayed windows for light and defence. A spiral staircase in the southwest corner connects the floors, winding past various chambers including a second-floor garderobe and mural chamber within the south wall. The third floor served as the main living space, originally lit by five windows, with the western one later converted to a fireplace. Evidence suggests this floor once had access to spiral stairs leading to the wall walks above, though the battlements, gables, and most of the defensive features have long since fallen. Only a single corbel remains of what was once a bartizan at the northwest corner.

The castle’s history connects it to both religious and secular powers of medieval Cork. Listed among the possessions of St Mary’s Abbey, Fermoy in 1541, it may have had earlier connections to the O’Hennessy family; an O’Hennessy served as abbot of the abbey in the late 15th century. Archaeological surveys have identified the remnants of a bawn wall following an irregular line around the tower, enclosing an area roughly 50 metres north to south and 20 metres east to west. Remarkably, Dunmahon Castle is almost identical in design to the nearby tower house at Curraghoo, suggesting they may have been built by the same patron or mason, though the exact circumstances of its construction remain lost to time.