The ringfort that once sat on a gentle south-west-facing slope in north County Cork was levelled in 1966, and the pasture that replaced it gives no hint that anything ever stood there. Yet aerial photography has since revealed the site as a soilmark, the buried outline of a bank with what appears to be an entrance to the north and traces of a second inner bank to the east, ghosts of earthworks that survived for over a thousand years before being erased in a single season.

When the antiquarian Bowman recorded the site in 1934, it was still an imposing presence on D. O'Leary's land. He described a double-ramparted fort of roughly 35 yards in diameter, with an outer rampart standing six to eight feet high and an outer fosse four feet deep. Between the two rings lay an intervening fosse 36 feet wide, a substantial defensive gap. Even then, half the circuit of the inner rampart had already been levelled, with the remaining portion standing about three feet high. A ringfort, to explain the term briefly, is a roughly circular enclosure defined by earthen banks and ditches, the most common form of rural settlement in early medieval Ireland, typically dating from around the sixth to the tenth century. The doubled ramparts at Mullaghroe placed it among the more elaborately defended examples of the type. By 1937, when Broker noted it separately, the site carried the name Lios na Duinne, and local tradition still spoke of the two rings surrounding the fort. The Ordnance Survey had mapped it consistently across three editions, in 1842, 1904, and 1938, each time showing the circular enclosure and its outer fosse. There may also have been a souterrain, an underground passage or chamber often associated with ringforts and used for storage or refuge, on the north side of the interior, though its condition is unrecorded.