It is not a natural cave. What the mapmakers were recording was almost certainly a souterrain, an artificially constructed underground passage or chamber built from drystone walling and covered with large flat lintels. Souterrains are found throughout early medieval Ireland, typically associated with ringforts and cashels, a cashel being a stone-walled enclosure of the kind that surrounds this feature, and were used variously for storage, refuge, or ventilation of adjacent structures.

The souterrain here has largely collapsed, leaving a sunken depression measuring roughly 1.8 metres east to west and one metre north to south, sunk to a depth of about 0.7 metres. The northern edge is still defined by drystone walling, and one original lintel remains where it was placed, presumably centuries ago. A second stone slab lies nearby, apparently displaced from its original position above the passage. The collapse has not entirely erased the souterrain's extent. A linear disturbance in the ground surface runs approximately six metres to the north-east from the sunken area, heading towards the remains of what may be two small houses within the same cashel complex, suggesting the underground passage continued in that direction. A large slab protruding at an angle from a shallow hollow about three metres to the north may be yet another remnant of the same structure, its tilt hinting at the slow subsidence of whatever void once lay beneath it.