This is a souterrain, a type of stone-lined underground chamber or tunnel built into ringforts across early medieval Ireland, most likely for storage, refuge, or both. What makes the one at Raheennamadra particularly arresting is what was found inside it during excavation: a hearth, an iron leather-scoring tool, animal bones, bone combs, and just outside to the north-east, two human skeletons, each with an iron knife blade placed to the right of the skull.

The site sits in an area known locally as Óenach Clochar, which the antiquarian T. J. Westropp, writing between 1917 and 1919, described as an ancient Celtic ceremonial landscape, comparing it to Tara, Telltown, and Brugh na Bóinne in County Meath, and to nearby Knockainey Hill in Limerick. The ringfort itself was excavated in 1966 by the Swedish archaeologist Marten Stenberger, who uncovered roughly four-fifths of the enclosure and cut sections through the bank and fosse, the defensive ditch surrounding the earthwork, to the west, east, and south. Near the centre of the interior he found the remains of a round hut with a hearth radiocarbon-dated to around AD 520. The souterrain, built against the inside of the southern bank and oriented roughly north-north-west to south-south-east, produced radiocarbon dates from its entrance postholes of approximately AD 520 and AD 690, suggesting the site was in active use across several generations of the early Christian period.

The ringfort lies in pasture approximately 115 metres east of the townland boundary with Mitchelstowndown North, and remains clearly visible in aerial imagery, including on Google Earth. Because it sits in agricultural land, access depends on landowner permission. The earthwork's circular bank is the most legible feature from ground level; the souterrain itself is no longer accessible to visitors. Anyone with an interest in the wider ceremonial landscape Westropp identified would find it worth looking also towards Knockainey Hill, which rises nearby and adds further context to what was clearly a significant stretch of early medieval Limerick.