Not a symbolic boundary, but a real one: a V-shaped fosse, up to three metres deep and seven and a half metres wide at the top, dug clean across the neck of the promontory to isolate whatever lay beyond it. A fosse is simply a defensive ditch, typically dug as part of an early fortification, and this one is precise enough in its geometry to suggest deliberate, organised effort. There is no causeway crossing it. Access into the interior was by a small path that ran down one side and up the other, a deliberately awkward arrangement that would have slowed any unwelcome visitor considerably.

The site appears on the 1920 edition of the Ordnance Survey maps under the label "Dun", the Irish word for a fort or fortified place, and it received a brief mention from the antiquarian Thomas Johnson Westropp in 1914. Westropp noted a wall some eight feet thick running along the inner face of the fosse, though little of that survives today. The only trace is a slight rise to the southeast of the ditch. The interior itself, roughly twelve metres in diameter and rising gently to a central point, is otherwise featureless. What makes the site quietly thought-provoking is a detail about what has been lost rather than what remains: sea rocks lie just six metres below the eastern edge of the interior, suggesting that coastal erosion has eaten into the structure over the centuries and that the fort was once considerably larger than it now appears.

The site sits in an area of rough grazing and tillage, overlooked by higher ground to the inland side, which means it was never a position of commanding elevation. Its strength was always the sea on three sides and the ditch on the fourth. Visitors approaching from the direction of Dooega will find the headland open and exposed, and the fosse itself, though worn by time, is still clearly legible in the landscape.