On Illaunloughan, a terraced mound of earth and stone rises to about 1.5 metres, scattered with white quartz, and at its western edge stone steps ascend to a rough-paved platform. There, a gable-shrine, essentially a house-shaped reliquary formed from two slate side-slabs averaging 1.3 metres by 1.1 metres, once enclosed something carefully hidden: two small stone-lined cists, each containing neatly stacked exhumed human bones, scallop shells, and white quartz pebbles. The end-slabs are gone, the north slab has slipped, and the whole structure is poorly preserved, but the deliberateness of what lies beneath it is unmistakable.

Four seasons of excavation between 1992 and 1995 uncovered approximately 70 per cent of the island and revealed that the shrine is a multiperiod structure, meaning it was built, used, and reworked over several centuries. Radiocarbon dating of bone from the cists placed one individual in the early seventh century and a second in the middle of the eighth. Beneath the mound itself, three rock-cut graves predate the construction entirely, suggesting that a sacred focus of some kind existed on the island before the present shrine was raised. The bones in the cists appear to be translated relics, meaning they were deliberately exhumed from elsewhere and redeposited here, a common early medieval practice for honouring a saint's remains. The island's name may itself reflect this: Lochán is mentioned twice in the Martyrology of Oengus, written around AD 800, and may refer to a founding saint associated with the site, though no historical documentation for the island survives. East of the shrine mound, at least five monks were buried in extended east-west inhumations, their heads to the west, seemingly seeking proximity to whoever lay in the cists. The scallop shells scattered throughout the shrine carry their own ambiguity. Some were perforated, possibly for suspension on cords. The scallop is the emblem of St James of Compostela, whose shrine in north-western Spain rose to pilgrimage prominence in the eleventh century, and their presence at Illaunloughan may point to a later refurbishment of the monument with that symbolism consciously in mind.

The gable-shrine at Illaunloughan belongs to a small cluster of similar reliquary monuments on the western Iveragh Peninsula, with comparable examples recorded at Killoluaig, Kilpeacan, and Killabuonia. These shrines are generally thought to mark the graves of monastic founders. The leacht, a rectangular terraced platform of earth and stone that forms the base, is a type of commemorative monument found at early Irish ecclesiastical sites, typically used for prayer and veneration. The island sits about 400 metres west-north-west of Portmagee village, close enough to see from the shore but separated enough to have kept its early medieval character largely intact.