That ambiguity is precisely what makes it interesting. Two filled-in ditches and levelled earthen banks, running parallel to one another across the wide neck of land connecting the headland to the rest of the island, have long invited a second look. The banks sit roughly six metres apart, which is a curious spacing for a simple agricultural division but consistent with the kind of widely-spaced earthworks seen at coastal promontory forts elsewhere in Ireland. A promontory fort, for those unfamiliar with the form, is an enclosure that uses natural coastal geography as its main defence, cutting off a headland with one or more earthen or stone banks and ditches rather than enclosing a full circuit of ground.

The site was noted by Christine Casey in her 2003 survey, which recorded the feature with careful caution. Casey acknowledged that the most straightforward reading of the parallel banks is that they represent a levelled field boundary, and the surrounding context does nothing to dispel that possibility: the area is given over to landscaped gardens and fertile pasture. Yet the doubling of the feature, with two elements running straight across the isthmus in close formation, nudges the interpretation toward something more deliberate. Adding further texture to the location is a medieval moated site sitting approximately 130 metres inland, overlooking the headland. A moated site, typically a raised platform surrounded by a water-filled or damp ditch, signals high-status occupation in the medieval period, and its proximity here at least confirms that this corner of Lambay has a long history of human use and territorial marking. The interior of the putative fort is described as featureless, and the sea is easily accessible from within.

Lambay Island itself lies roughly five kilometres off the Dublin coast and is privately owned, meaning access is not straightforward and requires prior arrangement. Visitors who do reach the island should approach the southwestern shore with the awareness that the earthworks are subtle and heavily levelled; there is no dramatic rampart to read against the skyline. What remains is a gentle swell in the ground, legible mainly to those who know what they are looking for. The proximity of the moated site inland is worth bearing in mind as a navigational reference point, and taken together the two features sketch out a landscape where successive generations found reasons to hold and demarcate this particular headland.