These are leachts, a form of devotional cairn associated with penitential circuits, and the fact that people were still walking rounds at them in the nineteenth century says something about the tenacity of practice in a place so difficult to reach. Illauntannig is the largest of the Magharee Islands, which occupy the stretch of water between Brandon Bay and Tralee Bay, and the settlement it holds is remarkably intact for somewhere so exposed.

The enclosure is bounded by a cashel wall, a term for a dry-stone enclosure of the kind common to early Irish monastic sites, and within it the full range of an Early Christian island community survives: two small oratories, three bee-hive huts (corbelled stone cells built without mortar), a souterrain, which is an underground stone-lined passage probably used for storage or refuge, a burial ground, and a stone cross. Finds from within the enclosure include three cross-slabs, a bullaun stone (a boulder with one or more natural or worked hollows, often associated with ritual use), a hand-bell, and fragments of five quern-stones used for grinding grain. A second bullaun stone sits roughly a hundred metres to the south, close to the sea's edge. The three leachts themselves are oriented roughly north-north-east to south-south-west, range from about 3.9 by 4.4 metres to 5.25 by 4.25 metres, and stand around a metre high. Across the water on the nearby headland of Reennafardarrig, a hut-site, old field walls, and a reputed cross-inscribed boulder may represent an outlying part of the same settlement.