A bullaun stone is a boulder with one or more cup-shaped hollows ground into its surface, associated in Ireland with early ecclesiastical sites and sometimes with folk cures or ritual use. That such a stone predates everything else visible here, the church included, hints at a much older sanctity attached to this particular slope.

The community here was a house of Arroasian nuns dedicated to St Mary, documented from 1195 to 1400. The Arroasian order was a reformed branch of the Augustinian canons, introduced to Ireland in the twelfth century and closely associated with the reforming bishop Malachy of Armagh. Drumalagagh was a daughter house of Clonard in County Meath, but around 1223 its affiliation was transferred to Kilcreevanty in County Galway. By the time of the Tudor suppressions the house had already been abandoned, and by 1641 the land, amounting to around 357 profitable and 147 unprofitable acres, was in the hands of the Earl of Clanrickard. The church that survives is a substantial structure for its setting: the west gable still stands to about six metres, with a low ground-level window and a second light placed high in the wall, and both north and south transepts remain partially upright. Curiously, there is no visible chancel extension, giving the building its unusual T-shape. Later cross-walls, now reduced to their foundations, suggest the ruins were reused or subdivided at some point after the community left.

The wider site rewards careful attention. South of the church, a stone-faced mill-race threads across the slope toward a nineteenth-century mill about 500 metres away, fed from a large rectangular building whose eastern end is still visible. A second large building to its west is remembered locally as a church. Built into its north corner was a sweat-house, a small stone structure, roughly 1.6 by 1.4 metres internally, of the kind once used across rural Ireland for therapeutic sweating, though this one has since collapsed. The remnants of a small field system to the north-west, its banks still associated with lazy-bed ridges, add a layer of post-medieval agricultural life to a place that had already accumulated several centuries of occupation before the nuns ever arrived.