It is only thirty centimetres high, roughly sixteen and a half metres north to south and fourteen metres east to west, with its opening facing east. Easy to walk past, easy to dismiss as a quirk of the landscape, it is in fact a fulacht fia, one of the most common and least understood monument types in the Irish archaeological record.

Fulachtaí fia are found in their thousands across Ireland, typically dating from the Bronze Age, roughly 2000 to 500 BC, though some examples are earlier or later. The mound itself is the accumulated waste of repeated cooking episodes: fire-cracked stone, charcoal, and scorched earth, built up over many uses into the characteristic horseshoe shape. The working method involved heating stones in a fire, then dropping them into a water-filled trough to bring the water to a boil, a process that cracks and blackens the stones and eventually renders them useless, after which they were discarded to the side. The trough itself, usually timber-lined and dug into the ground, rarely survives, but the mound of spent stone endures. The proximity to water was essential, and at Dromdeer the site sits immediately beside what was once a spring, now dry, in ground that remains marshy, preserving the wet, low-lying conditions typical of where these sites are found throughout the country.