At Coolies in County Kerry, this depression marks the remains of a souterrain, an underground stone-built passage or chamber of early medieval date, typically constructed beneath farmsteads for storage or refuge. It sits in the south-western quadrant of a cashel, a type of stone-walled ringfort, and nudges up against what may once have been a hut site along its north-eastern edge. The compression of features here, souterrain, cashel wall, possible dwelling, hints at a small but layered settlement whose surface traces are now little more than lumps and hollows in the turf.

The most vivid record of the site comes from the 1930s, when a Captain D. B. O'Connell visited and spoke with a local guide who had actually been inside one of the two chambers. That guide reported that the chamber led southward, which, if the passage followed a typical configuration, would have placed its far end somewhere beneath or beyond the cashel interior. O'Connell also noted something curious a short distance to the west of the souterrain entrance: a circular mound roughly two and three-quarter metres in diameter, with a large flat stone lying just fifteen centimetres below the surface. Whether that stone capped another feature, sealed an entrance, or was simply a coincidence of geology, O'Connell did not say, and the question has not been resolved since.