On the summit of Knocknarea Mountain in County Sligo, the surveyors marked a circle of boulders and annotated it confidently as a "Stone Circle". What it almost certainly is, however, is something rather different: a small enclosure or possible hut site, sitting quietly in the heather between two passage tombs, its low stone bank so heavily colonised by vegetation that its true character went unrecognised for well over a century.

The structure consists of a roughly circular area about nine metres in diameter, defined by a stone bank somewhere between three and four metres wide and no more than sixty centimetres high at its tallest. There is a gap in the bank on the north-western side, which may have served as an entrance. The overall external diameter reaches seventeen metres. Immediately to the north of the bank, a flat square area, roughly eight metres on each side, is defined on its western and northern edges by a shallow ditch about two metres wide and half a metre deep, left open to the east. What the structure was actually used for remains uncertain; Stefan Bergh, writing in 1995, catalogued it as a possible hut site or small enclosure rather than a ceremonial monument. Its neighbours make the location remarkable regardless of its own function: it sits fifty metres to the north of Maeve's Cairn, the enormous unexcavated passage tomb that dominates the Knocknarea skyline, and thirty metres to the south of a second passage tomb. A passage tomb is a prehistoric burial monument in which a long stone corridor leads to a central chamber, typically covered by a large mound of stones or earth. Whether the enclosure has any functional or chronological relationship to either tomb is not yet known.