It measures roughly six metres east to west and fourteen metres north to south, its edges indistinct, its surface broken into two sod-covered rises with a shallow depression of about three metres between them. That depression is the detail worth pausing on: it may mark the site of a trough, which would identify this as a burnt mound, the physical remnant of a prehistoric cooking or heating method practised across Ireland for thousands of years.

Burnt mounds are among the most common prehistoric monuments in the Irish landscape, yet they are easy to overlook precisely because they look like nothing much at all. They form when stones are heated in fire and then plunged into water-filled troughs to bring the water to a boil, a process repeated until the stones crack and fracture and become useless. Over time, the discarded burnt and shattered stone accumulates into a mound, often horseshoe-shaped around the remains of the trough. The Irish term fulacht fia is sometimes used interchangeably with burnt mound, though strictly speaking it refers to a related but slightly distinct monument type. That distinction matters here, because there is a fulacht fia located approximately fifteen metres to the south of this mound. The proximity is striking rather than coincidental. Two further burnt mounds lie within roughly eighty to eighty-five metres to the north-west and north-north-east respectively, suggesting that this corner of Knockalegan saw repeated, perhaps sustained, prehistoric activity centred on this wet, boggy ground. Waterlogged and marginal land was not a drawback for people using this technology; it was a practical requirement, providing ready access to the water and fuel the process depended on.