Known locally as An Lios Mór, this is a bivallate rath, meaning a ringfort defended by two banks and their corresponding ditches rather than the single bank more commonly encountered across Ireland. The outer fosse, the ditch cut outside the outer bank, survives to nearly 1.8 metres deep and 3 metres wide at its base in the northern section, though elsewhere it has been almost entirely filled in over the centuries. The outer bank itself rises around 2.1 metres above that fosse and runs between 6 and 7 metres wide at its base. The whole structure is substantial, with an interior measuring roughly 31 metres by 36 metres, and it sits high enough to command clear views across the surrounding landscape in every direction.

The antiquarian John Windele visited and recorded the site in 1848, noting two souterrains, underground stone or earth-cut passages associated with early medieval ringforts and typically used for storage or refuge, as well as a hut-site at the centre of the enclosure. One of the souterrains was earth-cut, the other stone-built, and between them they had two entrances, one opening into the interior and one into the fosse itself. Most intriguingly, Windele recorded that one of the structures reportedly contained a stone bearing what he described as round letters, a tantalising detail that has never been fully explained and cannot now be verified, since neither souterrain is any longer traceable above ground. A later field survey by J. Cuppage, published in the 1986 Dingle Peninsula archaeological survey, found the interior occupied only by stony mounds and hollows forming no legible pattern. The original entrance to the ringfort faces south-east, with a gap of roughly 1.8 metres through the inner bank and 2.1 metres through the outer, though the latter is now blocked by a modern wall. The north-east entrance is a later, secondary addition. The outer bank's south-western half still serves a practical function as the boundary line between the townlands of Knockavrogeen East and West, a neat example of ancient earthworks being quietly absorbed into the administrative landscape of later centuries.