This is a cashel, a type of early medieval ringfort defined by a drystone perimeter wall rather than an earthen bank, and the one at Kilwullaun measures roughly 47 metres across. What makes it particularly interesting is not just its survival but the way generations of agricultural life have accumulated around and over it. Rubble cleared from surrounding fields has been stacked against the outer wall-face across much of its northern and eastern arc, and a field boundary cuts straight through the monument at two points, treating it as a convenient structural feature rather than a relic to be preserved.

Within the interior, three distinct features have been recorded. There is a souterrain, an underground stone-lined passage or chamber associated with early medieval settlement sites, typically thought to have served for storage or concealment. Alongside it is a clochán beag, a small stone structure of the corbelled type found at various early Christian and secular sites across the west of Ireland. A rectangular house, orientated east to west and measuring 14 metres long by 8 metres wide, also sits within the enclosure; it is described as possibly later in date than the cashel itself, suggesting the site continued to be used or reoccupied after its original construction. Together, these features point to a place that was not simply built and abandoned, but returned to, adapted, and gradually absorbed into the working farmland around it.