The cashel at Rathcosgry, roughly thirty metres across, is the kind of site that rewards patience and a willingness to read the ground carefully, because on the surface very little announces itself. A cashel is a ringfort built from stone rather than earthen banks, and this one is defined by a wall that has been so thoroughly buried beneath field-clearance rubble, the accumulated debris of generations of farmers tidying their land, that its original form can only be traced rather than seen.

The interior of the enclosure is uneven, and in the eastern sector there is what survives as a possible house site, a depression or arrangement of stones suggesting domestic occupation at some point in the early medieval period, when cashels of this type were typically in use. More intriguing still is what McCaffrey recorded in 1952: a souterrain associated with the site. Souterrains are underground stone-lined passages or chambers, usually built during the early medieval period and associated with food storage or refuge. McCaffrey noted its location in detail, but no surface trace of it now survives, which means it either collapsed inward or was sealed by subsequent agricultural activity. A later field wall running east to west abuts the cashel at its northern side, a reminder of how later land management has continuously reshaped and obscured earlier boundaries without entirely erasing them.