It is easy to miss, and yet it was almost certainly placed there deliberately, at eye level on the approach to the main doorway, where anyone arriving at the castle would pass directly beneath it. The figure is a sheela-na-gig, a category of medieval carving found on Irish and British ecclesiastical and secular buildings that depicts a female figure explicitly displaying an enlarged vulva. Their precise function remains debated, with scholars variously proposing apotropaic, fertility-related, or cautionary interpretations, but their placement at thresholds and entrances is a recurring feature.

According to researcher Sherlock, writing in 2004, the carving at Fantstown is positioned on the eastern face of a quoin stone, with the figure's head oriented towards the arris, the sharp outer edge where two faces of the stonework meet. The quoin itself appears consistent with the surrounding stonework, which led Sherlock to conclude that the carving is likely an original feature of the structure rather than a later addition or reused stone. The figure is carved in false relief, meaning it sits within a defined outline rather than projecting fully from the surface. It has a rounded head with a long face that tapers to the chin, with the shoulders meeting the jaw directly and no visible neck. The arms are bent at the elbows and lie close to a thin torso, with the hands resting on the upper thighs. The legs are slightly bent at the knees, with the right leg more bent than the left, and the feet turned outward. Sherlock notes that breasts appear to have been intended, and that the large vulva is visible even from ground level. Whether the figure is meant to be standing or lying with legs splayed is left open.

Fantstown Castle itself carries the national monument reference LI048-004----. Visitors approaching from the north-east will find themselves on the same path the carving was designed to overlook, which is the most direct way to observe it in its intended context. Because the figure is carved horizontally along the quoin rather than upright, it rewards a careful, close look rather than a glance from a distance. The carving's subtlety in its positioning and its relatively quiet profile on the stone means it sits somewhere between architectural detail and deliberate statement, which may be exactly the point.