It measures roughly twelve metres across and rises only about forty centimetres above the surrounding ground. From a distance it could easily be dismissed as a natural undulation in the boggy terrain. But cut through its centre, where a modern field drain has sliced into the earth, the mound's true character is exposed: burnt stone embedded in charcoal-rich soil, the signature of a prehistoric burnt mound, or fulacht fiadh.

Burnt mounds are among the most common archaeological monument types in Ireland, found in their thousands, almost always beside water. The leading interpretation is that they were cooking places, where stones were heated in a fire and then dropped into a water-filled trough to bring it to the boil, though some researchers have suggested uses ranging from bathing to textile processing. The shattered, fire-cracked stones were raked aside after each use, gradually accumulating into the characteristic horseshoe or oval mound. The Rathslevin example sits precisely where such sites are typically found, beside a stream in damp, marginal ground. Another burnt mound of the same type lies just fifty metres to the north-north-west, suggesting this stretch of the stream was a place of repeated or concurrent activity at some point in prehistory, most likely during the Bronze Age.

The mound today is in a worn state. A cattle track has bitten into its south-western edge, and what appear to be shallow cultivation ridges cross its north-western half, evidence of later agricultural use that has further disrupted the original form. The field drain that bisects it, while damaging, is also the reason its internal layers of burnt stone and dark soil are now visible at all.