A round-arched window sits partly blocked on the nave's west wall, a later pointed window punched through beside it; a doorway in the south aisle has been sealed up entirely. These small contradictions, visible in the coursed limestone masonry, are what make the building worth pausing over. It is not a single moment of construction but an accumulation of changes, each generation leaving its mark without fully erasing what came before.

The church stands on the site of an earlier monastery associated with St Canice, the sixth-century Irish saint better known for his connection to Kilkenny. The medieval parish church that replaced or absorbed that earlier foundation is of nave and chancel plan, a common arrangement in which the congregation occupied the longer nave and the clergy used the narrower chancel beyond. The chancel here was once lit by a double-light ogee-headed window, a late Gothic form characterised by its S-curved arch, and it retains a sandstone piscina along its south wall, a shallow basin used for rinsing liturgical vessels, as well as a pointed-arched aumbrey, a small wall recess for storing sacred objects. In the south-east corner of the chancel, two seventeenth-century graveslabs survive: one commemorates Richard Treswell, who died in 1672, and the other, dated 1647, belongs to the Ryves family. Both slabs outlasted the active life of the building they were placed in, and they remain among the more legible details on the site.

The church sits at the edge of the Finglas East plateau, with a valley opening to the east, which gives the ruin an unusually open aspect for what is now a suburban Dublin setting. The west gable of the nave is heavily buttressed and carries a round segmental arched window with a circular window above it, details that are easiest to read from a little distance. The south aisle, entered through wide round arches supported on pillars, rewards closer inspection for its blocked doorway. Visiting in winter or early spring, when vegetation has died back, makes the structural details considerably easier to follow.