No earthwork rises from the ground, no stones mark its edge; the only evidence of this structure is a cropmark, a phenomenon where buried features cause overlying crops or grass to grow at slightly different rates, revealing outlines that are otherwise invisible at ground level. That telltale ring was captured in an aerial photograph taken in July 1989, showing the fosse, or defensive ditch, of a circular enclosure roughly twenty metres in diameter.

A ring-ditch of this kind is typically understood as the eroded remnant of a once more substantial enclosure, possibly a ringfort or a burial monument, its banks and ditches reduced by centuries of agriculture until nothing remains visible from the ground. The Knockacappul example sits in a landscape that appears to have held more than one such feature. Approximately two hundred metres to the north-east lies a possible ringfort, a separate site that raises the quiet suggestion that this corner of north Cork was, at some earlier period, a place of some local significance. Whether these two features were ever related in function or in time, the available evidence does not say.