It measures roughly ten metres east to west and six metres north to south, rising no more than about seventy centimetres above the surrounding ground. To a passing walker it might look like nothing more than a slight rise in a damp field. To an archaeologist, the blackened, fire-cracked material that makes up its bulk tells a different story.

The mound is a fulacht fia, a type of prehistoric cooking or heating site found in great numbers across Ireland, particularly in low-lying, waterlogged ground. The typical interpretation is that water was heated by dropping stones, fired in a nearby hearth, into a trough; repeated use would crack and shatter the stones, and the accumulated debris was heaped into the characteristic horseshoe-shaped or oval mounds that survive today. The site at Rossanean fits the pattern well. A drain carrying water runs immediately to the north of the mound, likely a remnant of the original water source that would have made the location practical. The archaeologist M. J. O'Kelly, whose 1954 study of fulachtaí fia became a foundational reference for Irish prehistoric studies, included this site in an appendix to that work, suggesting it was recognised as a significant example even then. O'Kelly's research, much of it carried out through excavation at sites in County Cork, helped establish the basic sequence of how these monuments were used and how their distinctive mounds accumulated over time.