Not ruined, not repurposed, not quietly absorbed into a later building; simply unlocated. Its existence is recorded, its builders are known, and yet the ground has so far declined to give it up.

The castle's origins lie with the Cistercians, the monastic order who established a significant presence across medieval Ireland following their arrival in the twelfth century. The Cistercians were unusual among religious orders in their appetite for practical infrastructure, and a castle associated with their holdings would not have been out of character for the period. According to Healy (2004), the structure at Kiltiernan was built by the Cistercians and remained standing until the dissolution of the religious houses in 1540, when Henry VIII's suppression of monasteries swept away monastic landholdings across Ireland as it had in England. Turner (1983) also records its previous existence, though neither source has been able to pin down precisely where within Kiltiernan the building once stood.

For anyone visiting the area, the honest answer is that there is nothing specific to see. Kiltiernan is better known today for its portal tomb, one of the largest in Ireland, and the broader landscape repays careful attention to those interested in the deep archaeology of the Dublin Mountains foothills. The absence of the castle is itself a kind of puzzle worth holding in mind as you walk the area; fieldwork, local knowledge, and future survey work may yet bring it to light. Researchers with an interest in monastic landscapes or medieval settlement patterns in south Dublin may find it a worthwhile thread to follow, even if the loom is, for now, missing.