A fulacht fia is a type of ancient cooking or industrial site, typically consisting of a horseshoe-shaped mound of fire-cracked stone accumulated beside a water source, where water in a timber or stone trough was heated by dropping in stones from a fire. They are among the most common prehistoric monuments in Ireland, yet individual examples are easily lost to farming, drainage, and development. At Glenmagoo, the mound itself was levelled sometime in the 1950s, decades before anyone had formally documented it.

What remained when the site was identified in 1987 was a spread of burnt stone and charcoal measuring roughly five metres north to south and four metres east to west, lying in boggy ground close to a small stream. The location fits the classic pattern for these sites: low-lying, formerly marshy ground, near a reliable water source, at the foot of a slope. The marshy ground had since been reclaimed for agriculture, which explains both the site's setting and the earlier levelling of its mound. The fact that any trace was identified at all owes something to the persistence of burnt and shattered stone in the soil, material that resists disappearance even when the earthwork above it is gone.