The second edition corrected the error, though it retained only the 'Cave' label, which is, in its way, the more interesting of the two annotations. What the mapmakers were gesturing at is a souterrain, an underground stone-built passage system of the kind constructed during the early medieval period in Ireland, typically associated with ringforts and used for storage, refuge, or both. The earthen enclosure above ground is easy to underestimate: a U-shaped bank of earth and small stone, its eastern side closed off by a modern field wall, rising barely a metre above the surrounding ground at its highest point. Measuring roughly 15 metres north to south and 18.6 metres east to west, with a bank that splays out to a basal width of 6.5 metres, the interior appears level and featureless. The real complexity lies beneath it.

The souterrain opens through the external face of the bank at the south-west and extends 20.7 metres in total, divided into five separate passages. Its walls are of drystone construction, slightly corbelled, meaning the stones are angled inward as they rise to narrow the gap before flat roofing lintels are laid across the top. The current entrance, a tight 76 centimetres by 46 centimetres, leads into the first passage, which curves north-west for 6.2 metres. A small blocked opening in the south-west wall, just 1.2 metres inside, may represent the souterrain's original entrance, later sealed and replaced. The passages are separated by various deliberate obstacles: a large slab hanging from the roofing lintels to within 60 centimetres of the floor between the first and second passages, and a low lintelled creepway only 60 centimetres high giving access to the third. The second passage is the tallest and widest, reaching 1.9 metres in height, and contains a narrow shaft in its west wall that was probably an air-vent. The fourth passage has an uneven rock floor, and the fifth section has collapsed. A large perforated slab sitting in the centre of the enclosure above ground appears to overlie this final section and may once have served as a second point of entry into the system from above.