This is a fulacht fia, a type of monument found in considerable numbers across Ireland, typically consisting of a horseshoe-shaped or subcircular mound of fire-cracked stone surrounding a sunken trough. The usual interpretation is that water in the trough was heated by dropping in stones from a fire, though archaeologists continue to debate whether cooking, bathing, textile processing, or some combination of uses was the primary purpose.

The Kilmacshane example measures roughly ten metres northwest to southeast and just over five and a half metres on the other axis, with the burnt mound material best preserved at its northeastern and southeastern edges. A shallow depression toward the northwest, measuring around three and a half metres across and only ten to fifteen centimetres deep, likely marks where the trough once sat, though it has not been excavated to confirm this. The characteristic paired projections, or horns, that often frame a fulacht fia trough are not fully traceable here because a later hut or house site has cut into the monument from the northwest, leaving one portion of the monument truncated and its outline incomplete. What makes the site particularly notable in its local context is its position as the easternmost of four fulachta fia in the immediate area, suggesting that this stretch of Galway countryside was a focus of repeated prehistoric activity rather than a single isolated episode.