It is overgrown now, built from earth and stone, and measures roughly seventeen and a half metres across its longer axis. Around its base runs a shallow fosse, the term for a man-made ditch that typically served as a boundary or a first line of definition for whatever lay inside, and on the north-eastern side there are faint traces of what may once have been a causeway crossing that ditch.

Enclosures of this kind are scattered across the Irish countryside in considerable numbers, and their purposes varied: some were ringforts, used as defended farmsteads from the early medieval period onwards; others served ritual or territorial functions that are harder to pin down. At Keernaun, the combination of a raised interior, a surrounding fosse, and a possible causeway entrance follows a pattern well established in the Irish archaeological record, though the site has not been excavated and its precise date and function remain unconfirmed. What the location does suggest is a degree of deliberate choice: whoever built here understood the landscape well enough to identify the one patch of ground that would stay above the waterline when the surrounding grassland was submerged.