At Kincullia in County Galway, there is nothing to see, and that, in its own way, is the point. Somewhere beneath the northern half of a rath, the circular earthwork enclosure common across early medieval Ireland, lies a souterrain, an underground passage or chamber typically constructed from stone and used for storage, refuge, or both. It appears on the 1838 edition of the Ordnance Survey six-inch map, marked simply as "Cave", which suggests local people knew it well enough to name it. At some point after that map was drawn, the entrance was filled with stones, and today no surface trace survives.

The 1838 OS six-inch series was among the most detailed cartographic undertakings of its era in Ireland, and the fact that this feature was recorded on it at all gives a rough outer boundary for when it was still accessible, or at least remembered as such. The rath it sits within was clearly a significant local landmark; souterrains are frequently found in association with raths, and the pairing suggests a settlement of some substance in the early medieval period. Whether the blocking of the entrance was deliberate, precautionary, or simply the slow work of neglect and collapse is not recorded. Local information passed down over generations confirmed the souterrain's existence, but by the time that knowledge was gathered, the ground above had closed over entirely.