The structure, roughly D-shaped and measuring about sixty metres along its straight side, appears to have been raised not around a dwelling but around a hole in the ground. A large natural depression, known locally as a sluggera, occupies most of the interior, and the working theory is that the enclosure was constructed specifically to protect or demarcate it.

A sluggera is a local term for a natural hollow or soft ground, often associated with boggy subsidence, and the word itself points to the way such features were once treated as things that warranted attention rather than dismissal. The depression at Ardaprior measured approximately thirty metres northeast to southwest and twenty metres across at its widest, taking up nearly the whole interior of the enclosure except for a strip along the northeast side. The townland boundary curves closely around the site from east to south, which is itself suggestive; boundaries in Ireland frequently preserved the outline of older features, whether deliberately or by long habit. A low earthen arc, surviving as a slight rise of around 0.2 metres on the interior and 0.35 metres on the exterior, runs concentric with that boundary, with a shallow depression of about one metre on the outer face. It is modest in scale, easy to overlook in pasture, and made stranger still by the fact that the sluggera it may once have enclosed has since been filled in, removing the very feature that might explain why the earthwork was built in the first place.