Oilithir is an Irish word for pilgrim, and the building's popular title, recorded in anglicised form as 'Olther', preserves a memory of devotional traffic to this remote Atlantic site that the physical remains alone would not immediately suggest.

The church is late medieval in date and remarkably compact, measuring just 5.3 metres long and 4 metres wide, oriented roughly northwest to southeast and positioned at the mouth of Cuan an Fhir Mhóir. Despite its modest scale it retains several architectural details worth attention: a chamfered, pointed-arch doorway set into the southwest wall, and a plain window in the southeast gable with an altar beneath it. Chamfering, the cutting away of a sharp edge at an angle, was a common decorative treatment in late medieval ecclesiastical stonework, and its presence here points to a building that was finished with some care rather than purely functional intent. More intriguing are the beam-holes visible in both the northwest and southeast gables, which indicate that the church once had a loft, an unusual feature in a structure of this size. The seventeenth-century Connacht scholar Roderic O'Flaherty noted the building, describing it as the 'Pilgrime's church', a reference preserved in James Hardiman's 1846 edition of O'Flaherty's work on west Connaught. That a scholar of O'Flaherty's standing thought it worth naming tells us the church had a recognised identity, even in a landscape where small ecclesiastical ruins were commonplace.

The site sits within a graveyard that remains in use, so the surrounding ground retains its community function long after the church itself fell out of regular service. The setting directly on the shoreline, with the inlet of Cuan an Fhir Mhóir opening out nearby, gives the ruins an exposed, littoral quality that is inseparable from whatever drew pilgrims here in the first place.