It cannot be seen from the ground at all; it only becomes legible from above, when dry summers draw the buried outline of an ancient enclosure up through the grass as a cropmark, the differential growth of plants over disturbed soil tracing a shape that has been invisible for centuries.

The enclosure at Carrowkeeny measures approximately thirty metres by thirty metres, a neat, almost symmetrical square. Cropmarks of this kind form when buried features, such as ditches, walls, or pits, affect how deeply roots can grow, causing the vegetation above them to respond differently to drought stress. The result is a ghostly plan of a structure that left no surface trace. This particular site was reported by Jean-Charles Caillere and is detectable on aerial imagery from March 2011. What the enclosure originally was, who built it, or when, is not recorded, though its square form sets it apart from the far more common circular ringforts that define early medieval settlement across Ireland. Ringforts are typically circular earthworks enclosing a homestead, and one such site lies roughly ninety metres to the east-south-east in the adjoining field, suggesting this corner of Roscommon saw repeated, layered occupation over time. Whether the two features are contemporary with one another or separated by generations is an open question.