That label, plain and unexplained, refers to a souterrain, an underground stone-lined passage or chamber typically built during the early medieval period in Ireland, often as a place of refuge or storage and usually associated with a nearby settlement. The souterrain here sits within a rath, a circular earthen enclosure, the kind of defended farmstead that once dotted the Irish landscape in considerable numbers.

The souterrain is no longer accessible, but its presence can still be read in the ground. A linear depression in the western half of the rath interior, running roughly nine and a half metres north to south and about six metres east to west, and sinking to around half a metre in depth, traces the outline of what lies beneath. At the southern end of this hollow, there is a more pronounced dip, filled in with stones, which local tradition identifies as the original entrance point. It is a quiet kind of archaeology: the structure itself has collapsed or been sealed, and what remains is essentially its shadow, a soft geometry pressed into the earth close to the inner face of the enclosing bank.

The gap of nearly a century between the two map records that note the "Cave" suggests it was a recognised local landmark for generations, named and passed down even as the underground passage itself became unreachable. The stone-filled hollow at the southern end is perhaps the most legible part of the site today, a place where the accumulated weight of local memory and practical geology arrive at the same point.