Forty-five metres to the south-west, however, sits something considerably less photogenic and considerably more mysterious: a fulacht fia, or ancient cooking place, set on a natural rock terrace on the southern slope of a low hill. The term fulacht fia, sometimes rendered fulacht fiadh, refers to a class of prehistoric and early historic monument found across Ireland, typically identified by a mound of fire-cracked stones accumulated over repeated use. They are among the most common archaeological features in the Irish landscape, yet their precise social function remains debated.

Excavation of the Drombeg example, carried out by Fahy in 1960, revealed a surprisingly elaborate arrangement. At its centre was a slab-lined cooking pit and a U-shaped hearth, along with a well fed by an associated overflow drainage channel, a practical system for keeping water supply close to hand. Enclosing much of this was a horseshoe-shaped bank of drystone construction. Nearby, a C-shaped posthole structure surrounded an oval pit filled with burnt and broken stone, and a wedge-shaped roasting pit contained more of the same fire-fractured material. Radiocarbon dating of two samples produced results that complicated any simple narrative. Material from beneath the mound dated to somewhere between 109 and 349 AD, while a sample taken from the cooking pit itself returned a range of 368 to 608 AD. The gap between these two ranges spans up to five centuries, though the excavators concluded that intermittent use over several decades was a more plausible explanation than continuous occupation across half a millennium. Directly to the north of the fulacht fia lies an associated hut site, suggesting this terrace once formed part of a small but purposeful domestic complex, connected in some way to the stone circle that has since claimed most of the attention.