The structure is a souterrain, a type of man-made underground passage or chamber system commonly associated with early medieval Irish settlement, typically constructed to serve as storage, refuge, or a combination of both. What makes this one quietly arresting is the detail of its interior geometry: three distinct chambers connected by low crawlways, each one requiring a person to get down on hands and knees to pass between them, the whole system tunnelled directly into the earth rather than lined with stone.

The souterrain was recorded as early as 1906 by Cooke, and the measurements he and later surveyors compiled give a precise, almost claustrophobic picture of the space. Entry to the accessible portion was made through the collapsed roof of the northernmost chamber, an oval space roughly 2.1 metres long and just under 1.5 metres wide, its floor lying about 2.1 metres below ground level. A creepway barely half a metre high at its southern end leads into the largest of the three chambers, a subrectangular room some 3.7 metres long and 1.7 metres wide, aligned northwest to southeast. From there, a second creepway, only about 48 centimetres in both width and height, connects to a third chamber oriented east to west. That final chamber is partially blocked by collapse at its eastern end, leaving its full extent unknown. The dimensions throughout suggest a structure built for function rather than comfort, every transition between spaces deliberately narrow.