What appears at first glance to be a medieval fortification may actually be an elaborate 18th century folly, though the debate continues. The rectangular structure, measuring approximately 12.5 by 8 metres externally, sits within a circular walled garden on a gentle south facing slope in Dunran Demesne. Built from mortared granite and slate rubble without any cut stone, its walls rise to about 11 metres high and vary in thickness from 1.55 to 2 metres, featuring round corner towers and simple crenellations that crown all four walls.

The castle's interior reveals several curious features that fuel the ongoing debate about its origins. Two doorways provide access; one centred on the southeast wall and another at the southern end of the northeast wall. A rubble formed intramural staircase rises from beside the northeast door through the southeast wall, leading to upper floors where various windows and niches punctuate the thick walls. The ground floor contains three plain niches and several windows set in double splayed openings, whilst the upper levels feature additional windows and an intramural chamber. Notably absent are any corbels for supporting floor joists or other typical medieval structural elements, adding weight to the theory that this might be a later construction.

Historical records offer conflicting narratives about the castle's true nature. The Ordnance Survey Letters from 1838 to 1840 describe it as fully habitable during Lord Cornwallis's viceroyalty, even hosting a grand ball given by Mr. Grogan, complete with glazed windows; unusual features for a genuine medieval structure. Historian Price, writing in 1933, noted that whilst a castle appears on the 1652 Down Survey map positioned on a hilltop, the current structure sits halfway down a slope, suggesting it might be an "imitation antique" built around 1770 by General Cuninghame, later Lord Rossmore, as a romantic addition to his demesne. Whether Kiltimon Castle represents a genuine medieval fortress later converted into an 18th century folly, or was constructed entirely as a sham castle during the Georgian period, remains one of County Wicklow's more fascinating architectural mysteries.