Kid Island, known in Irish as Oileán Mionnán, sits just west of Benwee Head on the north Mayo coast, at the northeastern edge of Broad Haven Bay. That anyone chose to settle there at all is quietly remarkable; that the trace of their enclosure has survived the Atlantic weather is more remarkable still.

The structure is a rath, the Irish term for a ringfort, the most common type of early medieval settlement in the country. Ringforts typically consist of a circular bank and ditch enclosing a domestic area, and were used as farmsteads by farming families, probably between the sixth and twelfth centuries, though some were constructed earlier. This particular example sits on elevated ground at the northwestern end of the island. It is modest in scale, roughly 26.5 metres across, defined by a low earthen bank no more than 40 centimetres high and two metres wide at its broadest. Stone appears only occasionally within the bank, suggesting the builders worked primarily with what the ground gave them rather than importing material. The circuit is best preserved on the northwestern and northern sides; the eastern stretch has eroded away entirely, leaving a small pool of standing water where the bank once ran. Within the interior, on the western side, there are remains of what may be a house, offering a faint outline of the domestic life the enclosure was built to protect.

Access to Kid Island would require a boat, and the surrounding waters and coastline are exposed. The site is not easily visited, which may in part explain why this small settlement, perched above the Atlantic on an island most people have never heard of, has received so little attention.