A few stones poking through the ground, a vague swell in the earth, the faintest suggestion of a curve. It was only when Seán P. Ó Ríordáin began excavating in 1949 that the site revealed itself: a substantial cashel, the Irish term for a stone-walled ringfort, buried under centuries of collapsed masonry and accumulated domestic debris. The excavators were, by their own account, surprised. What had looked most unimpressive turned out to be one of the more carefully constructed stone enclosures in a county where such monuments are relatively uncommon.

Known as Carraig Aille II, the fort sits on a rock outcrop about 200 metres east of what was once a small lake, since drained in the 19th century, that formed part of Lough Gur. The cashel is not a tidy circle; its walls on the west and north sides run in almost straight lines, adapted to the shape of the underlying rock. Its greatest diameter, running southwest to northeast, is roughly 47.5 metres, and the rampart walls vary between about 3.65 and 4.3 metres thick, faced inside and out with well-shaped rectangular limestone blocks laid in broadly horizontal courses, with smaller stone spalls packed between them for stability. The entrance passage, just 1.5 metres wide, was the most carefully built section of the entire structure, paved on one side and cobbled on the other, with shallow recesses cut into each wall so that a gate, when swung open, could sit flush with the stonework. Steps were built into the inner wall at six points, most of them concentrated on the southern side where the ground was easier to approach and, presumably, where an attack was more likely. Ó Ríordáin estimated the wall originally stood somewhere between 1.8 and 2.4 metres high. Beneath the later stone paving inside the fort, traces of earlier, lighter round houses were found at the original ground level, their walls marked by little more than a single course of stones, along with post-holes cut into the rock, one of which still held the decayed base of a wooden post.

Carraig Aille II sits within a dense concentration of monuments around Lough Gur, including its neighbour Carraig Aille I about 40 metres to the north, a nearby settlement cluster, three additional stone structures excavated by the same team, and the remains of two crannógs, lake dwellings built on artificial islands, in what were once the Balie Islands of the drained lake. After excavation, the debris was not returned to the site; instead the ramparts were left exposed, with fallen stones repositioned only enough to even out the more collapsed sections. No restoration was carried out beyond what the evidence clearly supported, which means what you see today reflects the actual surviving fabric of the structure rather than a modern reconstruction.