It measures roughly ten metres from north-east to south-west and just over seven and a half metres across, rising to about sixty centimetres at its highest point. What fills it is not earth in any ordinary sense, but heat-shattered stones and soil blackened with charcoal, the accumulated debris of repeated, purposeful burning.

This is a burnt mound, a type of prehistoric site found widely across Ireland and Britain. The working theory, broadly accepted by archaeologists, is that these mounds formed beside a water source as stones were heated in fire and then plunged into a water-filled trough to bring it rapidly to the boil. The cracked and spent stones were then discarded to the side, slowly accumulating into the low, whale-backed mounds that survive today. The site sits on a gentle north-west-facing slope on the north side of a stream, precisely the kind of waterside setting these features consistently occupy. What makes Knocknakilla quietly notable is that it does not stand alone: two further burnt mounds lie within approximately 110 metres to the north and north-east, suggesting this particular stretch of ground saw sustained use over time, or perhaps by more than one group, clustered around the same reliable water source.