It is easy to miss. Roughly circular, no larger than a broad dinner plate and not especially deep, it has a single smooth hollow worn into its centre. This is a bullaun stone, a type of perforated or cup-marked boulder found at early Christian sites across Ireland, whose hollows were most likely used for grinding or ritual purposes and which were often associated with saints and sacred ground. The fact that this one sits practically at the gate, greeting anyone who enters, gives it an oddly prominent quality for something so understated.

The graveyard at Killulagh is associated with St. Lonán, whose feast day fell on the 12th of November, and the medieval parish church here may have been founded on the site of an earlier monastery attributed to him. Only the ivy-covered south-west gable of the parish church still stands, in the south-west quadrant of the enclosure. The graveyard itself is oval in shape, a form that often indicates pre-Norman origins, since early monastic enclosures in Ireland typically followed a circular or oval plan before the rectilinear conventions of later ecclesiastical building took hold. The bullaun stone, measuring roughly 0.3 metres by 0.26 metres and 0.14 metres in depth, with a hollow about 0.15 metres across at the top, sits on the north side of the entrance alongside the octagonal shaft of the medieval font, the two objects together forming a small, accidental archive of different centuries of religious practice at the same threshold.