It is only 2.8 metres long, a metre wide, and thirty centimetres high, lined with stones and roofed by five flat slabs. This kind of low stone-lined passage is known as a souterrain, an underground or semi-subterranean feature typically associated with early medieval ringforts, though here it runs at or just above ground level rather than below it. Their purpose is still debated, with theories ranging from food storage to refuge, but their presence in a site almost always signals that whoever lived here was thinking carefully about concealment or security.

The ringfort itself is a modest but legible example of the type. A roughly circular enclosure, measuring about 25 metres north to south and 26 metres east to west, it is defined by a low earthen bank no more than 0.7 metres high, faced with stone on its inner side. Ringforts, known in Irish as raths when formed from earth and bank rather than stone, were the dominant settlement form of early medieval Ireland, typically dating from roughly the fifth to the twelfth century. Thousands survive across the country, though many are fragmentary. At Cregg, the southern half of the bank has been partially obscured by dumped rubble and encroaching vegetation, which partly explains why a site with a genuine souterrain can sit in an ordinary field without drawing much attention. The situation of the enclosure is worth noting: it occupies ground with a commanding view southward across rolling West Cork countryside, a position that would have made practical sense for a farming household alert to what was coming over the hill.