Built from coursed masonry with carefully dressed corner stones, the square tower rises to stepped battlements, with a distinctive projecting angle tower tucked into its northwest corner. A string course runs around the building at parapet level, marking where the defensive battlements begin, whilst the walls show a subtle outward slope at their base; a common defensive feature that helped deflect projectiles and strengthen the structure’s foundation.

The castle’s interior reveals the practical considerations of medieval life and defence. Entry through the western side is now obscured by a Victorian house built directly against the ancient walls, but once inside, visitors would find themselves beneath a vaulted ceiling on the ground floor, its construction still showing traces of the original wicker-work centring used to support the stonework during building. A spiral staircase winds upward through the angle tower, providing access to the upper floors where daily life once unfolded. The first floor contains a garderobe, essentially a medieval toilet built into the wall thickness, whilst the second floor sports angle loops in the southeast and southwest corners; narrow openings that allowed defenders to fire arrows or crossbows whilst remaining protected behind the thick stone walls.

By the time of Cromwell’s Civil Survey in 1654 to 1656, the castle was recorded as having a thatched house adjoining it, suggesting that even then, the austere medieval tower was being supplemented with more comfortable domestic quarters. This gradual adaptation over the centuries, from defensive stronghold to residential complex, mirrors the story of many Irish tower houses as the country moved from medieval warfare to more settled times. Today, partially masked by its Victorian addition, Robswalls Castle remains a tangible link to Dublin’s medieval past, its weathered stones holding centuries of coastal history.