The centrepiece is an unusual T-shaped church, a layout that includes both north and south transepts but, strikingly, no chancel extension at the east end. The west gable still stands to about six metres, with two windows set at very different heights in the wall. Nearby, within twenty metres of the church, are five small circular stone spreads that may be hut-sites, though they might equally be the remains of field clearance. Two bullaun stones, large boulders with cup-shaped basins deliberately hollowed into their surface, are associated with the site, one lying about seventy metres to the south-west of the church. These stones are typically linked to early medieval religious activity and water-based ritual, and their presence here pre-dates all the other visible remains.

The community that used this church was a house of Arroasian nuns dedicated to St Mary. The Arroasian order was a reformed branch of the Augustinian canons that spread into Ireland during the twelfth century, and Drumalagagh appears in records as a daughter house of Clonard in County Meath, with references spanning from 1195 to around 1400. Around 1223, the connection shifted when the house was transferred to Kilcreevanty in County Galway. By the time of the Dissolution of the Monasteries in the sixteenth century, the community had already been abandoned, and by 1641 the land was in the hands of the Earl of Clanrickard. The later cross-walls inside the church, now reduced to foundations, suggest the building was adapted after the nuns had gone, its spaces subdivided for purposes no longer recoverable.

The surrounding landscape carries its own layers of activity. About 150 metres to the south-east, grass-covered foundations adjoin a mill-race that once fed a nineteenth-century mill further downstream. A second structure nearby, locally regarded as a church, contains the footprints of two small clay-walled houses built within its walls, and a collapsed sweat-house, a small stone chamber used for therapeutic sweating, tucked into its north corner. About 200 metres to the south-west stands a four-roomed masonry building whose walls survive to one and a half metres, though curiously it shows no sign of any doorway. To the north-west, the remnants of a field system, including the ridged earthworks of lazy beds once used for potato cultivation, cover about two hectares, with a house site set directly on top of one of the old field banks.