Two parallel banks, each only about twenty to forty centimetres high and two metres wide, run in a shallow curve across the width of the island, with a fosse, a shallow defensive ditch, between them. Together they cut off the pointed southeastern tip of the island, forming a roughly triangular enclosed space of around seventy-five metres by sixty-seven metres. The natural vertical scarps along the island's landward edges serve as the other two sides of this triangle, and a rocky cliff on the northern and southeastern face rises five to six metres above the water. The result is an enclosure that borrows heavily from the island's own topography, letting the natural landscape do much of the defensive work.

The interior of this enclosed area sits on a small natural hillock with a flattened top, from which the ground falls away steeply to the south and west. This elevated platform, roughly twenty to twenty-five metres long, would have given whoever occupied it a commanding view in both directions along the river: north towards Killala Bay and south along the Moy's course. From that vantage point, Rosserk Abbey is visible just four hundred metres to the southeast, and Castleconnor hall-house, a fortified medieval residence, sits on the eastern bank of the river a little further in the same direction. That combination of natural elevation, river control, and lines of sight to two significant medieval structures suggests the enclosure's position was anything but accidental. A gap of five to six metres near the centre of the curving bank arc may be the site of an original entrance, though erosion has also opened smaller breaks between the bank terminals and the island's edge, complicating any reading of the original layout.

The island lies approximately one hundred metres from the western bank of the river and can be reached on foot at low tide, making it accessible without any particular difficulty. The enclosure occupies the southeastern tip, the narrow pointed end of the island that juts furthest into the channel, so approaching from the west brings you first to the broader northwestern end before the banks and fosse come into view as you move along the spine of raised ground.