The roofless shell of a Church of Ireland building from the 1770s sits inside the nave of a much older structure, while a large 18th-century mausoleum fills most of what was once the chancel. Above it all, the partial remains of a crossing tower still rise, its south wall long since fallen, its east and north walls pierced by plain pointed masonry arches. A cruciform church, in which four arms extend from a central crossing like a cross, once occupied this ground in full; today only fragments of that plan survive, enough to read the outline but not enough to fill it in.

The origins of the cruciform building are uncertain. It may have begun as a Dominican friary in the 13th or 14th century, though no record survives to confirm this. What the stonework does suggest is a significant rebuilding in the 15th or 16th century, possibly at the same time the roof of the chancel was lowered. The east window of that chancel, with its switch-line tracery rising from two mullions, was noted by researchers in 1918 and again in 1927 as almost certainly salvaged from the earlier structure and reset. The church eventually became the parish church of Castlelyons, dedicated to St Nicholas, and was recorded as being in repair in both 1615 and 1694. The Church of Ireland building that replaced it as a functioning place of worship was put up in the 1770s by the Barrymore family of nearby Castlelyons Castle; it was completely renovated and restored in 1899, then closed in the early 1960s. Details worth pausing over include the west doorway of the nave, where a pointed stone arch sits beneath a two-light window with ogee heads, the curved decorative profile associated with late medieval Irish stonework, and a sloping hood outside the door carried on a pair of tapering corbels. The blocked lancet windows in the nave walls and the two-light ogee-headed window in the north wall of the tower, now missing its central mullion, speak to the same period of craftsmanship, one that outlasted its building by several centuries.