Before the Romanesque builders raised the present church in the late twelfth century, this site is said to have held a monastery founded by Finnian of Clonard - one of the great figures of early Irish Christianity, traditionally remembered as the teacher of the Twelve Apostles of Ireland. The connection puts the religious use of this ground back into the sixth century, when monks were colonizing the Atlantic edge of Europe and Skellig Michael, visible from here on a clear day, was being chosen as one of the loneliest places they could find. Killemlagh would have been the mainland counterpart - a small community looking out at the islands their colleagues had taken on. Saint Finin's Well, dedicated to the same saint, still rises beside the sea just west of the church, where pilgrims once drank water that was supposed to have healing power.

What stands now was built late in the twelfth century, in the Romanesque style that was the architectural lingua franca of medieval Christian Europe. The walls are made of local stone, with the door and window dressings cut from a distinctive green stone of the district. The windows have rounded heads, the east window splaying wider at its sill than at its top - small architectural choices that placed this remote church inside the same visual vocabulary as cathedrals being built in France, England, and Spain at the same time. The antiquary P.J. Lynch, who described the church in 1909, noted that the shallow pitch of the roof beams suggested some later modification - perhaps a thirteenth-century reworking on twelfth-century walls. He also noted that the original west doorway had been filled in, replaced by an opening on the south wall. The building had been edited as well as built.

The church sits in a glen between two mountains - Knocknaskereighta to the northeast and Canuig to the southwest - and the graveyard is locally called Glen graveyard, after the parish church built alongside the older Killemlagh ruin in the nineteenth century. That nineteenth-century church is also now roofless, a second generation of ruin layered over the first. Around them the headstones stretch out across the grass, some readable and many not, marking generations of families from the Skellig Ring townlands who chose to be buried where the saint had been. Just south of the church stands an enclosure of upright stones known locally as the Pagan's Grave - a megalithic monument from much earlier, suggesting that this ground was sacred long before Finnian arrived. The Christian site was built next to a Bronze Age one. The successive religions used the same hill.

From the churchyard the Atlantic opens out across St. Finian's Bay, with Puffin Island a short way offshore and the Skelligs further out. The Skellig Ring drive passes close by, connecting Portmagee to the north with Ballinskelligs to the south. Most visitors stop briefly, walk through the open gateway in the ruined wall, look out at the sea, and move on. The church itself does not demand interpretation. The walls are clear about what they once were; the doorway is clear about where you would have entered; the empty east window frames the sky where an altar once stood beneath a roof. Whoever Finnian was, and whoever the masons were who finished his church seven centuries later, they all chose this view. Nine centuries of weather have only sharpened it.