A large portion of the fort's eastern side is now occupied by what is known locally as The Derk Hole, a naturally occurring sea inlet that cuts into the site and gives the whole structure an uncanny, interrupted quality, as though the landscape has been quietly arguing with the archaeology for centuries.

A ringfort, or rath, is one of the most common early medieval monument types in Ireland, typically a circular area enclosed by one or more earthen banks and ditches, and used as a defended farmstead. This example is more elaborate than most. The circular platform measures 33.5 metres in diameter and sits atop a mound that is partly natural in origin, rising between 1.7 and 5.5 metres depending on where you measure. The enclosing bank is substantial, 8.5 metres wide and 1.2 metres high, and there is evidence of deliberate stone kerbing along its internal foot and stone revetment, a facing of stone to stabilise the earthen mass, on its outer face. At the base of the mound runs a fosse, the defensive ditch common to ringfort construction, between 2.5 and 3 metres wide, with its own outer bank beyond it, also stone-revetted on the inner face. The outer bank has been levelled along the north-west to north-east arc, which may reflect later disturbance or simply the demands of the terrain. A gap of three metres in the inner bank on the north-east side, accompanied by a causeway, is thought to mark the original entrance to the enclosure. Within the south-east quadrant, there is a raised area with a hollow beside it, the purpose of which is not recorded.

What makes this site linger in the mind is not any single feature but the combination: a carefully engineered enclosure, built with stone revetment and a formal entrance causeway, positioned on a naturally dramatic mound directly above the sea, and now partially defined by a tidal inlet that would have meant nothing to its builders. The Derk Hole is indifferent to the archaeology it has consumed.