What visitors see today is a fascinating architectural puzzle: the ruins of an elegant six-bay, three-storey Georgian house that was literally built around a late medieval tower house. The original tower, dating from the sixteenth or seventeenth century, now forms the southern half of the later structure, its eastern gable still jutting proudly above the collapsed roof of the eighteenth-century additions. Historical records place the Fitzpatrick family here in the early 1600s, with either Barnaby or Brian Fitzpatrick residing at Watercastle during that period.

The medieval tower house at the heart of the complex is a substantial rectangular structure measuring 8.5 metres north to south and 10.5 metres east to west, with walls two metres thick built from roughly coursed limestone rubble. Its original entrance, now blocked, was a pointed limestone doorway on the western wall that led into a fortified lobby area complete with an overhead murder hole and a small guard chamber. From here, a mural passage in the north wall provided access to the main ground floor chamber via another pointed doorway, whilst a spiral staircase in the northwest corner connected all the upper floors. The ground floor chamber featured three single-light windows set into large segmental arched embrasures; the eastern window displays fine ogee-headed stonework with punch-dressed jambstones, though it was partially damaged when a doorway was inserted during the nineteenth century.

The transformation of this defensive structure into a comfortable Georgian residence occurred in the early eighteenth century, when according to O’Hanlon and O’Leary’s History of the Queens County, the old castle underwent repairs, was enlarged, and converted into a dwelling that became known as Watercastle House. During this renovation, the castle’s interior walls were rendered over, larger openings were created, and new floor levels were inserted. The original wooden floors throughout the tower were supported on timber wall plates resting on finely cut stone corbels with punch-dressing and drafted margins, typical of sixteenth or seventeenth-century craftsmanship. Today, the site appears on both the 1841 and 1906 Ordnance Survey maps as well as the earlier Down Survey barony map, standing as a remarkable example of how Ireland’s medieval fortifications were adapted and absorbed into the Georgian architectural landscape.