The mound is only 35 centimetres high, roughly ten and a half metres from north to south and five or six metres across, but its shape is quietly telling. It curves around what appears to be a trough area on its eastern side, which fits the classic pattern of a fulacht fia, a type of ancient cooking or processing site found in considerable numbers across Ireland. The method is thought to have involved heating stones in a fire, then dropping them into a water-filled trough until the water boiled. The discarded, heat-shattered stones accumulated over time into the characteristic horseshoe or crescent-shaped mound that survives today.

This particular mound sits on the western fringe of a patch of wet ground on a natural terrace, with the ridge rising steeply to the north-west behind it. The choice of location is typical. Fulachtai fia are almost always found close to water or marshy ground, and the wet terrace here would have supplied exactly what the process required. What makes Steelaun more than a single roadside curiosity is the density of related monuments in the immediate vicinity. Another burnt mound lies roughly 150 metres to the south-west, and a cluster of four more fulachtai fia or burnt mounds sits about 85 metres to the north. This concentration suggests the area was used repeatedly, perhaps seasonally, over an extended period. The mound at Steelaun is distinguished from the surrounding pasture not by its height but by subtle differences in vegetation: shorter grass and fewer rushes grow over the dense concentration of stone fragments and dark, charcoal-rich soil beneath the sod, marking it out to a careful eye.