This is a promontory fort, a type of defended enclosure found all around the Irish coast in which a headland's natural cliff edges do much of the defensive work, with a constructed bank and ditch sealing off the landward approach. What makes the one at An Cloigeann quietly odd is how modest its surviving defences appear against the drama of the setting: the main bank rises only 0.4 metres above the interior, the external fosse is barely 0.2 metres below the surrounding field level, and the sea itself is entirely inaccessible from within the enclosed space or from anywhere immediately nearby.

The enclosed area measures roughly 62 metres north to south along the bank and 47 metres east to west, sloping steeply down toward the western cliffs. The main bank runs straight for most of its length before curving inward near the northern cliff edge, possibly accommodating the natural fall of the ground. It carries an outer revetment of vertical stone slabs and is accompanied by a shallow fosse, the defensive ditch cut outside the bank, with traces of a low counter-scarp bank visible in places. Scattered outcrops and random stone settings across the interior suggest collapsed and grassed-over structures beneath the surface. Some 8 metres east of the main bank, and tucked into the base of a natural scarp that looks down over the fort, lie the remains of a drystone oval enclosure measuring 7 metres by 5.4 metres internally, with no clear entrance visible. This feature, interpreted as a possible hut site, sits on higher ground than the fort itself, in a position that would have commanded a clear view of the enclosed area below. The detailed survey of the site was carried out by Markus Casey as part of a 1999 MA thesis on the coastal promontory forts of counties Sligo, Mayo, Galway, and Clare.