It is a modest label, but in Irish archaeological terms it almost certainly points to something more deliberate than a natural hollow. A souterrain is a man-made underground passage, typically stone-lined, built during the early medieval period as a place of refuge, cool storage, or concealment. The word on that Victorian map suggests local memory of such a structure had survived long enough to be recorded by the surveyors, even if they did not quite know what to call it.

The rise on which the souterrain sits belongs to a wider enclosure known as Clahereen, a version of the Irish Cathairín, meaning 'little stone fort'. The site is a univallate cahir, that is, a roughly circular enclosure defined by a single enclosing bank, in this case a well-preserved earth-and-stone bank that remains clearly visible on the ground. Cahirs of this kind are associated with early medieval settlement in Munster, and their elevated positions were chosen with some care; this one commands a good view of the surrounding countryside. When archaeologists first examined the interior of the enclosure, three substantial house-sites were identifiable within it. By the time a follow-up survey was conducted, agricultural ploughing had erased them entirely. What had been legible as structural remains was gone, leaving only the bank, the rise, and the faint possibility of whatever still lies underground.