A souterrain is an underground stone-lined passage or chamber, typically built in early medieval Ireland as a place of refuge or storage and usually associated with a ringfort above it. Here, even the ringfort it belonged to has gone, leaving nothing visible to the eye and only the documentary record to confirm that anything was ever there at all.

The ringfort at Ardnageehy was already in a sorry state by the early twentieth century. Writing in 1917, a researcher named Power noted that it had been levelled and its souterrains partly destroyed, suggesting that agricultural clearance or land improvement had done considerable damage well before any formal archaeological attention was paid to the site. The plural "souterrains" is worth pausing on: it implies there was more than one underground passage associated with this ringfort, which points to a site of some original complexity, even if nothing of that complexity now remains above ground.