What makes it worth pausing over is the engineering concealed in its apparently simple form. The interior has been deliberately cut into the hillside on the eastern side and built up on the western side, effectively levelling the ground within the enclosure to create a flat, usable space on what would otherwise be an awkward gradient.

This is a rath, a type of ringfort common across early medieval Ireland, typically dating from roughly the sixth to the tenth century and used as a defended farmstead for a family of some local standing. At Knocknakilla, the enclosure measures 26 metres across in both directions, making it a fairly standard example of the form. The defining bank survives to an internal height of 1.2 metres along the northern to south-south-eastern arc, and is topped by a ruinous stone wall. Elsewhere, the boundary takes the form of a scarp rising to 2.5 metres, stone-faced in places, giving the site a more substantial presence than the earthen bank alone would suggest. A gap of 2.5 metres in the southern bank likely marks the original entrance. The field fences that once surrounded the site have since been removed, leaving it more exposed than it would have appeared in recent centuries. A record from 1937, cited by a writer named Broker, describes a fort on land belonging to a Dan Harrington, noting it as roughly a quarter of an acre in extent, with a fence finished with stone. That description matches closely enough to confirm the site had already attracted local notice well before any formal survey was undertaken.