A drystone wall, the kind built without mortar by stacking stone on stone, once formed a complete ring around the interior; what survives still measures roughly three and a half metres in width, suggesting it was once a substantial structure. The site is locally remembered as a 'fort', which places it in a long tradition of popular memory attaching significance to these enclosures long after their original purpose has faded.

The site belongs to the category of monument known as a cashel, which is essentially the stone equivalent of a ringfort, the earthen enclosures that dot the Irish countryside in their thousands. Where ringforts were typically built up from banks of earth and timber, cashels used drystone construction, and tend to survive in areas where stone was the more readily available material. The Cullion example retains traces of an outer wall at both the north-west and south-east, hinting at a more elaborate defensive or enclosing arrangement than the inner circuit alone would suggest. The original entrance has not been identified. A field boundary running north-west to south-east now cuts across the interior, dividing it into two unequal portions, which gives the site a slightly bisected appearance that obscures the original spatial logic of the enclosure.