A midden, in archaeological terms, is essentially a prehistoric rubbish deposit, the accumulated debris of meals eaten and shellfish gathered over time. What makes this one quietly arresting is its context: a tiny oblong island, just twenty-five metres from north to south and eight metres wide, rising barely two metres above the surrounding sand flats, with shell deposits visible at three separate points around its edges.

The island is named Doonanpatrick on Ordnance Survey maps from 1838 and 1922, and sits roughly 400 metres south-east of Coney Island, with the Killaspugbrone peninsula on the mainland about 700 metres to the south-west. It was recorded as a possible crannog, an artificial or artificially modified island typically built on a lake or estuary, in a 1995 heritage inventory, but a closer inspection in 2000 confirmed it as entirely natural in origin. That same 1838 map shows the island as a considerably larger feature, approximately fifty metres by thirty metres, compared with its present dimensions. A spread of stones extending fifteen metres outward across the surrounding sand flats is thought to preserve something close to the island's original footprint, the rest having been steadily consumed by wind and wave erosion. The three midden deposits around the island, one clearly exposed at the northern end with its oyster-rich layer, another visible at the south-western end, and a possible third on the western side, may originally have formed a single continuous deposit. The differing shell compositions at the north and south-west ends complicate that interpretation, but the island's small size makes it plausible.

The island is reachable at low tide, either across the sand flats from Coney Island or along the traditional causeway route that begins in Scardan More townland, about 1.8 kilometres to the south-east. The midden layer itself is exposed in section at the northern end, at a height of 1.1 metres above the shoreline, visible as a distinctly packed band of shells in the eroding face of the island. A portion of about a metre on its western side appears to have eroded away relatively recently, so what remains is already a reduced version of what once existed.