What survives of St. Mary's Augustinian Priory is not a ruin frozen at a single moment but a palimpsest of building phases, each generation of canons adjusting, inserting, and blocking what came before. A thirteenth-century window that once filled the entire east wall was bricked up and replaced by a four-light window with switchline tracery, probably in the fourteenth or fifteenth century. Narrow lancets, the tall slender windows typical of early Gothic churches, were punched through the chancel's south wall and later partially replaced by an ogee-headed window. A blocked round arch in the north wall was converted into a tomb recess, probably in the sixteenth century. The building's biography is legible in the stone itself, if you know what to look for.

The priory is said to have been founded by Gilbert Harvey in the early thirteenth century. It was built of rubble masonry with sandstone jambs, and its later additions, traceable in the shift to limestone, point to ongoing activity through the fifteenth and sixteenth centuries. By 1436 an indulgence had been granted to penitents who visited and gave alms toward repairs to the church, which suggests the building was already in need of attention at that point. The monastery was formally suppressed in 1542, though a small community may have lingered until the Desmond Rebellion of the 1580s, when the last canons appear to have dispersed. The property was subsequently granted to Sir Henry Wallop. A drawing published by Hewson in 1879 shows the west tower still standing to a considerable height and draped in ivy; today only about 4 metres of the north wall of that tower remains, along with a spread of rubble.

What survives today includes the south and east walls of the church, the chancel end of the north wall, and the ground floor of the north tower, where a barrel vault, a continuous curved stone ceiling, still spans the space. The south wall stands to about 8.5 metres in places, and its drainage course and chutes are relatively intact. The east gable retains its stepped profile almost complete, though the coping stones on the north side are gone. The priory sits on the edge of the town, and the remains are visible without specialist equipment or prior arrangement; reading the layers of construction, particularly the sequence of windows in the south wall and the changes visible in the east gable, rewards a slow circuit of the walls.