A rath, as these enclosures are known, was typically a circular earthen bank enclosing a farmstead, the standard unit of rural settlement in early medieval Ireland. At Knocknacaska, almost the entire bank has been levelled flat. Only one arc survives, running from the east-northeast around through east to south, and even that is no longer the original earthwork; it has been completely rebuilt in stone, with a steep drop on its outer face. What stands is less a relic than a reconstruction imposed on top of one.

The complexity deepens once you look inside. The interior contains a sub-rectangular house-site aligned northeast to southwest, measuring roughly 16 metres by 14.6 metres internally, with walls about 4 metres wide. Attached to its northeast corner is a further rectangular structure, 12.6 metres by 7 metres internally, suggesting the enclosure was modified or extended at some point. To the east and southeast of the main house-site sit two separate mounds of stone, their original purpose unrecorded. Immediately to the northeast, a quarry has clipped the edge of the site, which accounts in part for the difficulty of reading its original form. The surrounding landscape still falls away from the rise in every direction, giving the place the wide, supervisory outlook that made elevated ground worth enclosing in the first place. The description of the site draws on C. Toal's North Kerry Archaeological Survey, published in 1995, which catalogued the dense scatter of early monuments across this part of the county.

What makes Knocknacaska worth attention is precisely its ambiguity. The enclosing bank is gone or rebuilt, the interior structures are substantial but unexplained, and the quarrying has further complicated any reading of the ground. It is a site that resists easy classification, which is itself a kind of information about how long and how variously this particular patch of Kerry hillside has been put to use.