The Ordnance Survey mapped it in 1842 as a circular enclosure and labelled it 'Knoppoge Fort', yet the site resists easy classification. It is neither straightforwardly a fort nor a simple natural feature, and that ambiguity is part of what makes it quietly compelling.

The knoll itself is subrectangular, measuring roughly 75 metres on its longer axis, and has been deliberately terraced on its eastern and southern sides, with the terracing standing to a height of around 3.6 metres and a width of roughly 8 metres. The flattened top, about 15 metres in diameter, suggests some degree of human modification, and to the east there is a souterrain, an underground stone-lined passage of the kind associated with early medieval settlement in Ireland, typically used for storage or refuge. Writing in 1961, O'Mahony described the site as a tumulus, a burial mound, and recorded its local name as 'the cnapogue', from the Irish word 'cnapóg', meaning a small lump or knoll. The name 'Knoppoge' in the 1842 mapping is simply an anglicised rendering of the same word, suggesting the feature had a settled identity in local memory long before anyone tried to formally categorise it. Whether the terracing, the flat summit, and the souterrain represent successive phases of use, or a single period of activity, remains unclear, but the combination is unusual enough to give the site a character all of its own.