A fulacht fia is a type of prehistoric cooking site, typically identified by a horseshoe-shaped mound of fire-cracked stones and charred material left behind after repeated use. Water was heated by dropping stones into a trough, and the accumulation of shattered, burnt material over time is what survives. At Glenreagh, that spread of burnt material is still present, though the mound that once rose above the field surface was levelled around 1980, leaving the site far less visible than it once was.

What makes the situation at Glenreagh quietly interesting is the proximity of a second fulacht fia located roughly 80 metres to the south-east. Paired or clustered examples are not unheard of, and their closeness raises the kind of questions that rarely get answered: whether they were used at the same time, by the same people, or whether one simply succeeded the other across a long span of prehistoric activity. Both sites now sit in ordinary farmland, the kind of ground that has been worked and grazed over so many generations that their original landscape context is almost entirely obscured.