This former stronghold of the Cantwell family, who held sway here until the 17th century, presents an unusual architectural puzzle with its distinctive recessed southern wall and partially collapsed circular stair tower at the southwest corner. The castle’s strategic position alongside a public road, with quarries opposite and the remains of a medieval church just 50 metres to the southwest, speaks to its importance as both a defensive structure and administrative centre during its heyday.

The tower house tells a story of changing fortunes through its architectural details and historical records. John Cantwell, Lord of Mellisson, died in 1532 and was laid to rest in Kilcooley Abbey, but by 1640 the property had passed to Pierce Croake. The Civil Survey of 1654-6 describes it as an inhabited ‘castle and bawne’, whilst the Down Survey map shows it as part of a small settlement including the church and two dwellings. The building itself is constructed from roughly coursed limestone rubble with dressed quoin stones, entered through a doorway in the circular stair tower’s south face. What makes this tower house particularly intriguing is the pronounced external recess on its southern face up to second-floor level; above this, the upper wall projects outward, supported by corbels, creating an overhang that would have provided defensive advantages.

Inside, the ground floor features two narrow slit windows and curious blind arcades in the east and west walls, whilst the first floor, originally supported by wooden beams, sits beneath a barrel vault constructed using an innovative technique involving long vertical timbers running east to west. Evidence suggests the castle once had defensive bawn walls; remnants of one possibly extend westward from the southwest tower towards the church, though this may be associated with a later 18th-century house, whilst traces at the eastern angle indicate another wall running southward parallel to the modern road. Today, whilst the upper chambers remain inaccessible and the stair tower has partially collapsed, Mellisson Castle continues to dominate its hilltop position, a testament to the complex layers of Irish medieval and early modern history.