It measures seventeen metres long, twenty-two metres wide, and rises to about one and a half metres, with an opening six metres across facing to the north-east. To a casual eye it might look like a natural rise in the pasture, but it is in fact a fulacht fia, one of the most common yet least-understood monument types in the Irish landscape.

A fulacht fia is essentially the debris left over from a prehistoric cooking or heating site. The typical arrangement involved a timber trough sunk into the ground near a water source, which was filled with water and then brought to the boil by dropping fire-heated stones into it. Once cracked and spent, those stones were discarded to the side, building up over repeated use into the characteristic horseshoe or kidney-shaped mound that survives today. Thousands of these sites are known across Ireland, with particularly dense concentrations in Munster, and most date to the Bronze Age, broadly spanning the period from around 2000 to 500 BC. The north Cork example at Knockduff conforms closely to this familiar form, its opening in the mound corresponding to where the trough would once have sat. What the site was actually used for remains a matter of some debate among archaeologists; cooking meat is the traditional explanation, but proposals ranging from textile processing to communal bathing have also been seriously argued.