They were used variously for storage, refuge, or both, and are often found in clusters with ringforts and churches. The one at Kilcooly in County Galway is unusual not so much for what it contains as for the manner of its discovery, and the brevity of its known existence above ground. In 1992, a bulldozer clearing what was recorded simply as a "mound" broke into the structure entirely by accident, stripping away the roof lintels and exposing what lay beneath to daylight for the first time in centuries.

What emerged was a drystone-built passage of considerable length, more than 21.3 metres in total, running east to west across a prominent rise in undulating pastureland, roughly 100 metres south of a local church. Two chambers were connected by a narrow creep, the low constricted crawlway common to souterrains that would have forced anyone moving through to slow down considerably, an effective deterrent to anyone unwanted. The first chamber measured 3.9 metres long, 2.1 metres wide, and 2 metres high; the second was slightly narrower but similarly proportioned. Linear hollows filled with rubble suggested the structure originally extended further in both directions, meaning the bulldozing had not revealed the full extent of what had been buried there. Archaeologists were able to inspect the exposed sections, record the dimensions, and observe the drystone construction, but the window was short. Shortly after the site visit, the souterrain was filled in again, this time because the open chambers posed a danger to livestock grazing on the surrounding pasture.

The site sits in a landscape that still carries the faint topographical logic of its early medieval past, a rise near a church, the kind of pairing that recurs across the Irish countryside wherever souterrains have been found. There is nothing to see at Kilcooly now. The chambers are closed, the mound that concealed them is gone, and the field has returned to ordinary agricultural use. What makes the place worth knowing about is precisely that: a structure of real scale and craft, built to be hidden, accidentally opened, briefly seen, and closed again.