It measures roughly eighteen metres in length and over a metre in height, with a smaller, lower accumulation of burnt material gathered at the mouth of its opening like a threshold marker. The whole thing is easy to walk past without registering what it actually represents.

A fulacht fia is a type of prehistoric cooking site found widely across Ireland, typically dated to the Bronze Age, though some examples span earlier and later periods. The basic principle involves heating stones in a fire, then dropping them into a water-filled trough to bring it rapidly to a boil. The stones shatter and blacken with repeated use, and over time the discarded fragments accumulate into the distinctive curved or horseshoe-shaped mounds that survive in the landscape today. The fact that these sites cluster in low-lying, wet ground is no accident; proximity to a reliable water source was essential to the process. At Horsemount, the marshy setting fits this pattern precisely. The eastward-facing opening of the mound is a noted feature of many fulachta fia, though the reasons for this orientation remain a matter of some discussion among archaeologists.