There is no earthwork, no marker, no depression in the ground to suggest that anything unusual lies beneath. Yet just twenty centimetres below the surface, an underground stone-lined passage runs from northeast to southwest, invisible from above and unsuspected until a routine piece of farmwork brought it to light.

In December 1980, a large stone was disturbed during the removal of a field fence. When lifted, it revealed the entrance to a souterrain, the term for the dry-stone underground chambers and passages built, most commonly in early medieval Ireland, as places of refuge, storage, or concealment. The Knocknaneirk example was communicated to record by J.P. McCarthy, and its most striking feature is how close it sits to the surface, a mere 0.2 metres down, which makes its survival without any visible surface trace all the more remarkable. The fence removal was purely practical, with no archaeological intent, yet it inadvertently exposed something that had lain undisturbed and undetected, possibly for over a thousand years.