At ground level, the field gives nothing away. The land simply rises slightly, the grass continues, and whatever lies beneath remains invisible to anyone walking across it. What we know of this site comes entirely from a single aerial photograph taken in 1956, in which a circular, slightly raised area roughly twenty metres in diameter becomes legible as a shadow, its outline defined by a surrounding fosse and a faint external bank.

A barrow is a prehistoric burial mound, typically dating from the Bronze Age, built to cover the remains of the dead and to mark their place in the landscape with something deliberate and permanent. The fosse, a ditch dug around the mound, and the external bank beyond it are classic features of the form. At Coollegrean, those features are subtle enough that they register only in the particular light conditions and low sun angles that make aerial photography so useful for detecting earthworks that have been ploughed, grazed, or simply settled into near-invisibility over millennia. The 1956 photograph captured the site as what archaeologists call a shadow site, a feature revealed not by what stands above the ground but by the way slight differences in soil depth or moisture cause grass to grow in faintly distinct patterns, casting barely perceptible shadows at the right moment. The site is classified as a possible barrow, which reflects genuine uncertainty; without excavation or further survey, the circular form and its enclosure can be interpreted but not confirmed.