It is, in fact, a cashel, a type of ringfort defined by its stone enclosure rather than an earthen bank, and this one at Ardabrone preserves the outline of an early medieval farmstead that has been slowly dissolving back into the ground for well over a thousand years.

The enclosure measures twenty-six metres in diameter, its boundary formed by a spread bank of rubble limestone with larger boulders dispersed throughout. The bank now stands only around forty centimetres high on the interior and stretches to about one and a half metres wide, its original height and profile lost to centuries of collapse and gradual dispersal across the surrounding ground. No trace of a fosse, the external ditch that often accompanied earthen ringforts, is visible at ground level, and no upstanding sections of walling survive. Even the original entrance has been effaced beyond recognition. What makes the site quietly remarkable despite this erosion is a souterrain running beneath the bank at the north-west. A souterrain is an underground stone-lined passage, typically associated with early medieval settlement, and used variously for storage, refuge, or ventilation of a living space above. Its presence here suggests that whoever enclosed this hillside once invested considerable effort in making it habitable and defensible, even if the surface today gives little indication of that ambition.