What they found was a souterrain, a type of dry-stone underground passage common in early medieval Ireland and typically associated with storage or refuge, roofed by nine large slabs. Six of those slabs were inscribed with ogham, the early Irish script carved as a series of notches and strokes along the edges of stone. Bones and skulls, some reportedly human, were found inside. The whole structure had been quietly doing a second job as a burial space, or at least as a repository for the dead.

Ogham stones were raised, most commonly, as memorial markers during the early centuries of the first millennium AD, recording names and lineages in a formulaic style. To find them reused as roofing material is not entirely unheard of, but the Coolmagort group is remarkable for its concentration. One of the larger stones had cracked at some point in antiquity and was held in place by a seventh stone propped upright beneath it. That particular stone, now standing 2.65 metres tall and nearly half a metre wide, carries a well-preserved inscription along both of its edges: MAQI-RITEAS MAQI MAQI-DDUMILEAS MUCOI TOICACI, a genealogical formula identifying a person by their father's name and tribal affiliation. The scholar Macalister, writing in 1945, noticed a small pocked rectangular hollow on one edge of the stone and interpreted it as evidence that an erroneous character had been deliberately removed during the original carving. In 1940 the Office of Public Works removed the ogham stones from the souterrain and re-erected them beside a nearby public road. The underground chamber was filled back in and nothing of it now shows above ground.

The stones stand close to a public road in Coolmagort, near the Gap of Dunloe in County Kerry, accessible without any specialist access or permission. The inscription on this stone has since been recorded as part of the Ogham in 3D project run by the School of Celtic Studies at the Dublin Institute for Advanced Studies, which used photogrammetry to capture the carvings in precise digital detail, a useful counterpart to standing in front of the stone itself and trying to trace the cuts with your eyes.