That kind of deliberate orientation is easy to overlook in a ruin, but here the relationship between the opening and the liturgical furniture has survived intact, even as much of the rest of the structure has broken away.

The church at Killaspugbrone was originally a single undivided space combining nave and chancel, a common arrangement in early and medieval Irish ecclesiastical buildings before the functions of the two zones became more architecturally distinct. It measures just under fifteen metres in internal length and a little over five metres wide, and was built from very large, roughly coursed blocks of limestone and sandstone. Both gables are still standing, though the west gable has been heightened at some point, presumably during a later phase of use or repair. The south wall retains the remains of a flat-headed window near its east end, and high in the west gable there is another opening, now mostly broken out, with a simple recess cut into the wall on either side of it. The doorway, also largely broken away, sat in the west end of the south wall, the conventional position for an entrance in Irish medieval churches. On the north wall, near the east end, there is an aumbry, a small cupboard-like recess built into the wall to store liturgical vessels, and a niche to its south. The west end of the interior has been taken over by a mausoleum, a later addition that repurposed the space for burial rather than worship.