When excavators finally got inside this oval cashel, a type of stone-walled ringfort common in early medieval Ireland, they found the builders had enclosed a surface of jutting rock knolls and uneven outcrops rather than levelling the interior into anything obviously practical. The highest point of the hill was the point, apparently, and whatever inconvenience the broken ground caused was judged worth it. A small compartment discovered just inside the eastern entrance, less than 1.2 metres square, was so confined it could hardly have served any purpose other than sheltering a single sentry. Beside it, fragments of paving and traces of rectangular house walls survive, along with steps built into the rampart at two points to allow access to its top. Part of the northern rampart is missing entirely, removed by stone quarrying at some point after the fort fell out of use.

The site sits on a rocky outcrop about 200 metres east of where a small lake once lay, a lake drained in the nineteenth century that formerly formed part of Lough Gur. The submerged remains of two crannóga, artificial or modified islands used as dwelling places, are still traceable in what were once called the Balie Islands. The cashel itself was excavated by Seán P. Ó Ríordáin, whose 1949 report designated it Carraig Aille I to distinguish it from a second cashel lying just 40 metres to the south-east, which he called Carraig Aille II. Though Carraig Aille I looked more clearly defined before excavation, it proved the less substantial of the two once the soil came off. The fort wall ranged between 3.35 and 4.3 metres thick and the greatest overall diameter reached about 42.6 metres. Finds from the site were relatively sparse compared to its neighbour, the quantity of bronze in particular being, as Ó Ríordáin noted, meagre. An iron hand-pin may date to the seventh century, while beads with rope ornament point toward a tenth-century context. Ó Ríordáin concluded the two cashels were broadly contemporary, with Carraig Aille I likely the earlier of the pair, built first on the commanding high ground before the second fort extended the settlement downslope.

The Lough Gur landscape is dense with monuments and the Carraig Aille sites sit within a cluster that includes further excavated stone structures to the north-north-west. The cashel is a National Monument, number 247. Visitors approaching from the Lough Gur Heritage Centre will find the rocky hillside requires some care underfoot, and the uneven interior the excavators described is still very much in evidence. The entrance, facing east, retains its recessed jambs on either side, though the stonework is rougher than the corresponding features at Carraig Aille II. The second cashel is close enough to visit in the same circuit, and taken together the two forts give a clearer sense of how early medieval communities organised themselves across a hillside than either would offer alone.