The mound measures roughly fifteen metres along its northeast to southwest axis and twelve metres across the other way, rising only about sixty centimetres from the surrounding ground. Its opening, around two and a half metres wide, faces northwest. It does not announce itself.

This is a fulacht fia, a type of prehistoric cooking or processing site found in enormous numbers across Ireland, though the precise purpose of individual examples is still debated by archaeologists. The usual interpretation is that a trough was dug nearby, filled with water, and then heated by dropping fire-cracked stones into it. Those stones, once spent and shattered, were raked out and piled to the sides, which is what creates the characteristic horseshoe shape visible here. The burnt and blackened material that builds up over repeated use is what makes these mounds so recognisable in the landscape, and so durable. What makes the Derrynatubbrid example quietly interesting is that it does not stand alone. A second fulacht fia lies roughly ninety metres to the southeast, raising the question of whether the two were used at the same time, by the same community, or represent separate episodes of activity across a longer span of time.