The site was known in early medieval Irish as Tulach na nEpscop, meaning something close to "the hill of the bishops", and by the eighth century no fewer than eight bishops had been associated with it. That this quietly ruined granite church beside a county Dublin laneway was once a hub of ecclesiastical authority is not immediately obvious from what survives today, but the layers embedded in its stonework reward a closer look.

The church, commonly called Tully Church, is dedicated to St. Brigid, the fifth-century abbess of Kildare whose cult spread widely across early Christian Ireland. The fabric of the building reflects more than one period of construction. The nave, built from random granite blocks with dressed granite quoins, the carefully shaped corner stones that give a rubble wall its structural integrity, appears to be the oldest surviving element. The east wall of the nave was later modified to accommodate a chancel arch, dateable to the thirteenth century, beyond which lies the chancel proper, measuring roughly 8.5 metres long by 5.5 metres wide internally. The chancel is entered through a round arch and lit by deeply splayed round-headed windows in the east gable and side walls; bar holes are still visible in the window jambs, the slots that once held iron bars across the openings. A narrow ope, a small aperture in the wall, sits above the chancel arch and opens back into the nave, a slightly puzzling feature whose original purpose is not fully settled. The church also sits within a series of external enclosures, traces of which remain on the ground.

Tully Church is reached via a laneway in Laughanstown, to the south of Dublin city, in an area that feels distinctly suburban despite its mountain backdrop. The ruins are low but legible, and the granite construction gives the remaining walls a certain solidity even in their reduced state. The windows in particular are worth examining up close, as the depth of their splays and the quality of the stonework speak to a building that was, in its time, considerably more than a local parish chapel. Visiting outside the growing season, when vegetation is lower, makes it easier to read the ground-level features, including the enclosures around the church itself.