It is here, on the edge of that escarpment, that Cahergrillaun sits: a cashel, or stone-walled ringfort, whose positioning feels less like convenience than deliberate statement. The enclosure is roughly subcircular, measuring around forty metres across, and its double-faced stone wall still stands up to four metres high in places, with a pronounced outward lean, or batter, to the outer face that gives it a solid, almost monumental profile. The lower courses are built from stones roughly a metre long; the upper ones, probably added or replaced in a later period, are noticeably smaller.

The antiquarian T. J. Westropp visited the site in 1898 and left a careful record of what he found. He noted that the entrance, set into the south-east of the wall, was unusually wide, its passageway sided by massive flat stones laid lengthways, and he calculated that spanning such a gap overhead would have required wooden roof beams rather than stone lintels. He also recorded a narrow internal terrace running around the top of the inner wall-face, with at least one flight of five steps at the west leading up to what he described as a platform. Outside the cashel, he could make out the foundations of houses and smaller enclosures pressing against the north and south of the outer wall. When the site was inspected again in 1998, none of those external features were detectable, nor was there any trace of a possible souterrain, an underground passage sometimes used for storage or refuge, or a possible hut site that had been tentatively identified within the interior. The cashel sits within a larger, multi-period field system, and two other cashels lie within roughly two hundred and fifty metres of it, one to the south-south-west and one to the north-east, suggesting this part of the Burren was once a densely organised landscape rather than the spare emptiness it might appear today.