It measures roughly five metres east to west and three metres north to south, rising only about forty centimetres from the surrounding ground. What makes it worth pausing over is what it is made of: shattered sandstone fragments packed into a matrix of black soil, the kind of discolouration that comes from prolonged exposure to fire and water over many centuries.

This is a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, typically dating from the Bronze Age. The standard interpretation is that stones were heated in a fire, then dropped into a water-filled trough to bring the water to a boil, with the cracked and discarded stones accumulating over time into the characteristic horseshoe or oval mound. The preference for wet, low-lying ground was deliberate; proximity to a water source was essential to the whole process. At Carrowcaslan, the mound sits at the base of a gentle north-facing slope, right on the boundary of an area of wet, marshy ground, which fits the pattern closely. At the base of the mound there also appears to be a spread of levelled material, possibly suggesting earlier or associated activity at the site, though its precise nature is not fully resolved.