Measuring thirty metres east to west and nearly as long north to south, it rises to about one and a half metres, with an opening eight metres wide facing south-west. It is partially overgrown now, blending into the surrounding grazing land well enough to be easily overlooked. What it actually represents is one of the most common prehistoric monument types in Ireland, and one of the least understood.

A fulacht fia, sometimes called a burnt mound, is the remains of an outdoor cooking or processing site, typically Bronze Age in date, though many examples span a wide period of use. The usual interpretation involves a trough dug into the ground, often near water, which would be filled and then heated by dropping fire-cracked stones into it. The shattered, heat-blackened stones were raked aside after use, and over time these accumulated into the distinctive horseshoe or kidney-shaped mounds that survive today. The proximity of the Castlecooke example to a nearby stream fits this pattern precisely; access to water was a practical necessity, and these sites are almost always found close to a watercourse or wetland. Ireland has thousands of them, making them the most numerous prehistoric monument type in the country, yet the full range of activities they served, whether cooking, brewing, textile processing, or bathing, remains a matter of ongoing debate among archaeologists.