The feature measures roughly 23 metres north to south and 25 metres east to west, a generous footprint for what archaeologists call a fulacht fia, the term used for the characteristic mounds of fire-cracked stone that survive in their thousands across the Irish landscape.

A fulacht fia typically formed around a trough, usually timber-lined or cut into the ground, which was filled with water and then heated by dropping stones that had been fired in an adjacent hearth. The cracked and spent stones were raked aside after each use, and over generations these discards accumulated into the low, often horseshoe-shaped mounds that survive today. The Renny example sits within a wider field system, suggesting it was part of an organised agricultural or pastoral landscape rather than an isolated feature. That context matters: it places this particular spread of burnt material within a community that was managing land, not simply passing through it.