The 1840 Ordnance Survey map calls it the Baptism Church, yet by 1920 the same map series had revised this to Teampull na bhfear ngonta, a phrase roughly meaning the church of the wounded men, and marked it already in ruins. Scholars now lean towards reading it not as a baptistery at all, but as a mortuary chapel, a place set aside for the burial of particular classes of people. That quiet contradiction, a building whose name changed entirely between two editions of a map and whose original purpose remains open to argument, says something about how loosely the memory of early ecclesiastical sites can be held.

The structure sits in the northern part of what is known as the Saint's graveyard on Inis Cealtra, a monastic island in Co. Clare with a cluster of early medieval remains. The building is Romanesque in style, meaning it belongs broadly to the rounded-arch tradition that flourished in Ireland during the twelfth century, and is rectangular in plan, measuring roughly 5.8 metres east to west and 4.2 metres north to south. It was built on a plinth, with squared corner stones, called quoins, that project slightly from the wall face, and a matching squared feature running along the base of the walls just above the plinth line. The walls now stand to just under two metres at their tallest. There is no evident entrance, which in itself is strange, and the three openings that survive have prompted disagreement: Macalister, writing between 1916 and 1917, interpreted all three as entrances rather than windows. One of these openings, in the western wall, had an internal splay, a widening of the reveal on the inside, but has since been robbed out for its stonework. An altar at the eastern end is capped with large broken flags. The building was extensively reconstructed, probably around 1700, which may account for some of the confusion about its original layout and function.

Inis Cealtra is accessible by boat from Mountshannon on the western shore of Lough Derg, and the island is a national monument in state care. The Baptism Church stands within a graveyard that also contains several other early structures, so the site rewards careful attention to the ground underfoot and the relationship between buildings. The altar, the ambiguous openings, and the absence of any clear doorway make this small ruin more puzzling up close than it appears from a distance.