Yet on its rocky north-western headland, beneath a Martello tower and a thick covering of fern and bracken, there may be something considerably older waiting to be properly examined. Aerial observation has revealed what appears to be a promontory fort, the kind of enclosed defensive site, typically Iron Age in origin, that uses the natural topography of a headland to reduce the amount of walling or ditching required. The sea does much of the work on three sides; a fosse (a ditch, often cut into bedrock) and an accompanying bank or wall closes off the landward approach.

The features noted by Casey in 2003 are suggestive rather than conclusive. Some 30 metres inland from the tip of the headland, a curving natural escarpment of rock outcrop sits alongside a level berm and a gentle rise to the west, a combination that points to the likely presence of a fosse and an associated bank or wall. Several further, vaguer lines run across the headland closer to the Martello tower itself, possibly indicating additional phases of defence. The tower is an early nineteenth-century structure, one of the chain of squat circular fortifications built along the Irish coast during the Napoleonic period to guard against French invasion, and its construction may well have disturbed or obscured earlier remains. Crucially, as of Casey's survey, the site had only been assessed from the air and had not been visited on the ground, meaning the identification remains provisional.

The island is accessible by a short boat trip from Howth harbour, with seasonal ferry services running during the warmer months. Once ashore, the interior is dominated by dense bracken, which makes cross-country movement slow and obscures surface features considerably. The ruined church dedicated to followers of St. Nessan stands in the island's interior, a reminder that the Eye once supported an early Christian community. Visitors curious about the possible fort should make for the north-western point, where the Martello tower provides an obvious landmark, and look seaward and landward for any sense of the sloping escarpment and berm that caught an archaeologist's eye from the air. What you are likely to see is ambiguous; that, in a sense, is precisely the point.