It is a bullaun stone, a type of early medieval object found across Ireland, typically a boulder or slab into which one or more cup-shaped depressions have been worn or carved. Their exact purpose remains debated; they have been associated with ritual grinding, cursing stones, and holy wells, though in many cases their original function is simply unknown. What makes the Lusk example quietly notable is not so much what it is, but where it has ended up, and where it came from.

The stone was originally associated with the medieval church at Lusk, a site with early ecclesiastical origins. At some point it was moved, and it now sits outside the entrance to St Macculin's Roman Catholic church in the town. Its dimensions are modest: roughly 0.33 metres wide and 0.26 metres deep, sub-circular in shape, with a projecting lug on its southern side. According to Hunt, writing in 1974, the bullaun stone was once kept inside the round tower at Lusk alongside a 17th-century font and a portion of a carved fireplace taken from Bremore Castle. That fireplace piece was decorated in false relief with six shields bearing heraldic arms arranged around a depiction of the Annunciation, a detail recorded by Roe in 1979. The grouping of these objects inside the tower, each displaced from its original setting, gives a sense of Lusk as a place where fragments of different centuries accumulated around a single ancient core.

The stone is accessible to anyone visiting St Macculin's church in Lusk village, where it lies at the entrance. The medieval church and its distinctive round tower, which is unusually square at its base with the round shaft rising from it, are nearby and worth examining alongside the bullaun. The tower is one of the more curious ecclesiastical structures in north Dublin, and the broader site gives context to the stone's earlier home. The bullaun itself is easy to miss if you are not looking for it; it sits low to the ground and, without signage, reads more like a weathered garden feature than an artefact with medieval roots.