It measures nine metres long, six metres wide, and just over half a metre high, and it is made almost entirely of burnt, fire-cracked stone. This is a fulacht fia, one of the most common yet least-explained monument types in the Irish archaeological record, with thousands of examples recorded across the country. The horseshoe shape is typical: a hollow at the open end once held a wooden trough filled with water, into which heated stones were dropped to bring the liquid to a boil. The mound itself is simply the accumulated dump of those spent, shattered stones, discarded after each use.

Fulachtaí fia date predominantly from the Bronze Age, roughly 1500 to 500 BC, though some have yielded earlier or later dates. Their proximity to water is almost universal, which is why marshy ground and stream banks are such common settings. What exactly they were used for remains debated. Cooking is the most widely accepted explanation, and experimental archaeology has shown that the trough-and-hot-stone method can boil water surprisingly efficiently. Other theories include their use for bathing, textile processing, or brewing, and it is quite possible that different sites served different purposes at different times. The example at Tullig More, sitting on the northern bank of its stream, fits the classic profile in almost every respect.