A ringfort, or rath, is a roughly circular enclosure defined by one or more earthen banks, built primarily during the early medieval period in Ireland as a farmstead or place of refuge. This one at Caol Fuinseann is reasonably substantial, measuring just under 48 metres north to south, with an internal bank still standing to 2.25 metres in height. What lifts it out of the ordinary is the detail preserved within and around it: stone facing survives along the inner bank face, a causewayed entrance 5 metres wide opens to the south-east, and an internal undulation running roughly south-south-east to north-west hints at structural activity inside the enclosure that has not been fully explained.

The picture grows more interesting when older sources are consulted. Writing in 1898, a researcher named Murphy described the site as a very large fort with a double embankment encircling it. The outer bank he observed has since largely disappeared, but its ghost remains legible in the landscape. An Ordnance Survey six-inch map from 1904 shows a field boundary running along the line of the outer fosse, and that same boundary was still visible on the 1938 edition, suggesting local farmers incorporated the eroded outer earthwork into their field system rather than simply ploughing it away. The fosse itself, the external ditch that once reinforced the bank, is infilled across most of its circuit, though its outline can still be traced. Adding a further layer of interest, a rectangular feature sits off-centre toward the north-east inside the enclosure, measuring 15 metres by 12 metres, defined by a low bank with some upright stones used as internal facing and open on its eastern side. Its function is not recorded. A standing stone in the same field to the north-east suggests the broader area held significance across more than one period of use.