This headland, known as Dún Fiachrach, was once fortified across its narrow neck with multiple walls, ditches, and earthen banks, a layered defensive system that turned the natural geography into something approaching an island fortress. What makes it quietly remarkable is not just the engineering but the sheer redundancy of effort: wall behind wall, fosse behind fosse, as if whoever built here expected to be very seriously challenged.

A promontory fort works by treating the land itself as most of the defence, with only the narrow landward neck requiring artificial barriers. At Dún Fiachrach, that neck is fortified in depth. The innermost stone wall, built in random coursed limestone drystone masonry, still stands to 1.7 metres in places, with a defined entrance 1.1 metres wide set 6 metres from the northern edge. A berm, a flat ledge of ground separating a wall from its accompanying ditch, runs 2.5 metres wide before giving way to a fosse, a defensive ditch, that is 2.3 metres deep and 7 metres across, with a causeway just under 2 metres wide crossing it. Beyond this again, a second, shorter stone wall once stood, though most of it has since collapsed into the sea, taking its own external fosse with it. Further east still, earthen banks and traces of ditches continue the sequence. The antiquarian T. J. Westropp described the defences in 1912, and the deterioration since his account has been considerable; the ends of the inner wall, for instance, have crumbled away at both edges, leaving only low grassed banks where dressed stone once stood.

Inside the defences, the interior stretches 110 metres long and up to 40 metres wide. The ground is level towards the west but slopes downward as it approaches the landward barriers. Across much of the interior, the faint ridges and furrows of old lazybeds are still visible, the characteristic ridge-and-furrow pattern left by hand cultivation of potatoes. Some of these cultivation traces run directly to the cliff edge, hinting at ongoing coastal erosion that has already swallowed portions of the site. Two coves flank the headland below, reachable from just outside the fortified neck, and a freshwater stream runs down the cliff face nearby. This part of the Mullet coast holds at least two other fortified headlands in close proximity, suggesting that whoever used and defended these places did so as part of a wider pattern of territorial control along one of Ireland's more remote Atlantic coastlines.