A low, grass-covered rise, subcircular in shape and barely a third of a metre high, sits quietly inside the earthen enclosure. To an unpractised eye it might be nothing at all, but it marks the position of a souterrain, an underground passage or chamber of the kind built throughout early medieval Ireland, typically for storage or as a place of refuge.

Two openings in the surface of this rise, set roughly six metres apart, allow some glimpse of the structure below. The one to the north-east, roughly half a metre across in each direction, exposes an original stone lintel still in place above a passage that appears to run south-westward, though it is now largely filled with earth. The south-western opening is slightly larger and reveals drystone walling, the careful stacking of stones without mortar, along with what is probably another in situ lintel. The passage beneath it seems to extend northward or north-westward, though it too is partly collapsed or infilled. The two openings together suggest a connected underground system, though its full extent is no longer accessible. What gives the site a quietly curious place in the documentary record is its near-invisibility in the historical mapping sequence. The Ordnance Survey's six-inch map of 1837 makes no mention of it whatsoever. By the 1913 edition, something had been noticed, though whatever surveyor recorded it chose the ambiguous label of 'Cave', leaving its true character only partially acknowledged for another century.