It is a fulacht fia, a type of prehistoric cooking site found in large numbers across Ireland, typically identified by its crescent or horseshoe shape, its burnt and shattered stones, and its position near water or boggy ground. This one at Lugdoon is roughly circular, about twelve metres across and less than a metre high, with a central hollow and a composition of sandstone fragments packed into a dark, charcoal-rich soil.

Fulachtaí fia work on a straightforward principle: stones were heated in a fire, then dropped into a water-filled trough to bring it to boiling point, a method that leaves behind exactly the kind of fire-cracked stone debris found here. The charcoal-saturated matrix at Lugdoon is the residue of repeated burning over what may have been many generations of use. The site's location is typical of the type, sitting just above the waterlogged ground that would have supplied the trough, on the only patch of solid footing available. What makes Lugdoon particularly interesting is that a second fulacht fia lies just two metres to the south-south-east, suggesting this small island of dry land was returned to more than once, or perhaps used by more than one group at roughly the same time. Two such sites in such close proximity, both occupying the same narrow margin between firm ground and marsh, points to something deliberate in the choice of this spot within its valley.