The fort measures 44 metres north to south and 44.2 metres east to west, a near-symmetry that speaks to the care its builders took. What makes it quietly compelling is the way the interior has been deliberately levelled: the ground rises towards the north-east specifically to compensate for the natural slope of the hillside, so that anyone standing inside would have had a flat, usable space rather than a tilted one. That kind of deliberate earthworking is easy to overlook but represents considerable effort and planning.

This is a rath, the most common type of early medieval enclosure in Ireland, typically constructed between roughly the sixth and tenth centuries as a fortified farmstead for a family of some local standing. The defining feature is an earthen bank, sometimes accompanied by a fosse, which is a ditch dug outside the bank, the displaced soil going to build the bank up further. At Ardnageehy, a change in the incline of the bank from east to west suggests a fosse once ran along that side. The single entrance, 4.5 metres wide, faces east, a common orientation in Irish ringforts. There is also evidence of possible bank slippage along the north-north-west to north-north-east arc of the interior. Perhaps most intriguing is the suggestion of a souterrain in the southern half of the enclosure. A souterrain is an underground stone-lined passage or chamber, typically used for storage or as a place of refuge, and their presence within ringforts is well attested across Munster. The commanding view from the site, sweeping from north-west to north-east across the Cork landscape, would have made it a practical as well as defensible choice of location.