It measures roughly ten metres across in both directions, kidney-shaped, and its surface dips inward as though something has been scooped from its centre. What fills the hollow now is mostly reeds. What built the mound in the first place was fire, water, and a great deal of broken stone.

This is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, with several thousand recorded examples. The typical arrangement involved digging a trough near a water source, lining it, and heating stones in a nearby fire before dropping them into the water to bring it to a boil. The stones, repeatedly cracked by thermal shock, were discarded to the sides, gradually accumulating into the characteristic horseshoe or kidney-shaped mounds that survive today. The mound at Liscarroll is composed of exactly this material: heat-shattered stones mixed with charcoal-enriched soil, the residue of repeated use over what may have been a considerable span of time. The four-metre-wide opening faces west, which is consistent with the form, and the whole structure sits in the kind of low-lying, waterlogged ground that fulachta fia were routinely placed beside, proximity to water being essential to the process. The concave surface suggests that some material has been removed at some point, though whether by deliberate excavation or gradual disturbance is not recorded.