The enclosure itself is cut by a natural rock arch and sits to the south of Illaunamuck, Oileán na muc, which translates as the island of the pigs. Whatever activity once took place here happened at the edge of things, between land and sea, in a place where the geology has done much of the structural work.

The main enclosure consists of a stone wall that revetted, or faced and reinforced, a natural rock scarp, running for 34 metres with a maximum height of two metres both above the fosse and above the interior. A fosse is a defensive ditch, and here both the fosse and the bank curve convexly toward the landward side, suggesting the enclosure was designed to secure the headland from the inland approach rather than from the sea. What makes the archaeology here particularly layered is a note recorded by the antiquarian T. J. Westropp in 1909, who observed that the stones of earlier house-sites on the headland had been deliberately reused to construct the enclosure wall. In other words, one phase of settlement was dismantled to build the next, and the hut that survives in the north-west sector may represent only one moment in a longer sequence of occupation whose earlier fabric was absorbed into the very walls that now surround it.