The mound measures roughly nine metres in each direction, barely raising itself above the surrounding tillage, and its presence would go entirely unnoticed by anyone not specifically looking for it. These sites, known in Irish as fulacht fia, were once among the most common prehistoric monuments in the Irish landscape. The typical arrangement involved a trough dug into the ground, filled with water, and heated by dropping fire-cracked stones into it until the water boiled; the discarded, shattered stones accumulated over time into the characteristic mound that survives today. That accumulated debris is precisely what sits at Knocknamadderee, worn down to near-invisibility by centuries of agricultural activity on the north-facing slope.

About thirty-five metres to the west of the mound itself lies a spread of dark-coloured soil, a separate feature that may represent further activity connected to the same site. The dark staining is characteristic of the organic and charcoal-rich deposits that build up around prolonged burning and water use, and its separation from the main mound suggests the activity here extended across a small area of the hillside rather than concentrating at a single point. The site sits in land that has long been under tillage, which accounts for the low profile of the surviving mound; repeated ploughing gradually disperses and compresses the burnt stone spread, flattening what were once more pronounced earthworks.