Within a ringfort at Ballinluska in County Cork, there lies a souterrain, an underground stone-lined passage or chamber typically associated with early medieval settlement, used variously for storage, refuge, or ventilation of living spaces. What makes this particular example quietly remarkable is that it leaves no visible surface trace whatsoever. The ground above it gives nothing away.

The souterrain sits inside a ringfort, the circular earthwork enclosure that was the standard form of rural farmstead in early medieval Ireland, built and occupied roughly between the seventh and twelfth centuries. The association between ringforts and souterrains is well established; many such enclosures contain one or more of these underground structures, though they are frequently only discovered through excavation or accidental disturbance. At Ballinluska, the souterrain's existence was recorded by O Murchadha in 1967, who noted its presence without, it seems, any trace remaining above ground to confirm it visually.