Corbelling is a technique in which stones are laid so that each course projects slightly inward over the one below, eventually closing to form a roof without mortar or timber. The hut on Illaunloughan, known to excavators as Hut D, measures 4.4 metres internally and has an entrance just 0.9 metres wide facing east. What makes it peculiar is not merely its construction but its situation: a low-lying island with no historical documentation whatsoever, whose very name resists a clear reading.

Four seasons of archaeological excavation between 1992 and 1995 uncovered roughly seventy per cent of the island, and the picture that emerged was one of layered occupation stretching back well before the hut itself. Hut D was built over the remains of earlier stone huts, which were themselves preceded by a circular timber structure. Radiocarbon dating of animal bone from levelling dumps beneath the wall of Hut D gave a calibrated date of AD 775 to 961, placing its construction somewhere in the late early medieval period. Just to the south-east of the hut, excavators found a midden, the term for a refuse deposit, consisting of shells, bones, and charcoal, at least three metres long and overlain in part by a low drystone wall. Charcoal from this deposit returned an eleventh-century date, suggesting the site remained in use for generations. The midden also yielded fragments of an antler comb, bone beads, and two bronze ring-brooches, small but telling signs of a community that traded or travelled beyond the island. As for the island's name, Oileán Lócháin, one theory holds that Lochán was a saint whose memory is preserved in a church site called Killoughane at the eastern end of the Iveragh peninsula, and who appears twice in the Martyrology of Oengus, a calendar of Irish saints written around AD 800. The alternative, more prosaic reading connects the name to a word for chaff. Neither has been settled.