What appears at first to be a natural undulation in the land is in fact a carefully shaped enclosure, roughly circular, with an interior platform measuring about 24.5 metres east to west and 23 metres north to south. Structures like this are known in Ireland as raths or ringforts, earthen enclosures built predominantly during the early medieval period, between roughly the fifth and twelfth centuries, and used as defended farmsteads or the residences of local chieftains. This one at Edenmore has been sitting quietly in its field long enough to appear on the first edition of the Ordnance Survey six-inch map, published in 1837, where it is marked simply as "Fort".

The enclosure is defined by a combination of features that together tell a fairly coherent story of deliberate construction. On the north-east, south, and north-north-west sides, a substantial bank of earth and stone survives, between 5.5 and 6.5 metres wide and rising between 0.55 and 0.95 metres above the interior. On the remaining arc, the enclosure edge takes the form of a scarp, a cut or drop in the ground, here reaching 1.7 metres in height, likely where the natural slope of the hillside was incorporated and accentuated rather than built up separately. Running along the outside of the bank and scarp, from north-north-west around through north to south-east, lies a fosse, the term for the external ditch that typically accompanied such banks, here between 4.2 and 5.5 metres wide and still up to half a metre deep. Most telling is a gap of roughly 4 metres in the bank on the east-north-east side, which is thought to mark the original entrance to the enclosure, oriented, as was common, to catch the morning light.