It is a souterrain, an artificially constructed underground chamber or tunnel built from drystone walling and roofed with flat lintels, a type of structure associated in Ireland with early medieval settlement, most commonly used for storage or as a place of refuge. What makes this one worth pausing over is how precisely it has been recorded: five metres long, just over a metre wide, and tall enough for a crouching adult to move through.

The souterrain sits in the north-western quadrant of a rath, which is a circular earthen enclosure typically dating from the early medieval period, roughly the sixth to twelfth centuries, that would once have enclosed a farmstead or small settlement. Entry to the underground passage was made through a gap between two of the six roof lintels at its north-western end, a feature that may have served as a deliberate and defensible entrance rather than a later accident of the stonework. No corbelling, the technique of overlapping stones inward to create a vaulted ceiling, was used here; the roof is flat and lintel-borne throughout. Where collapse has occurred at that north-western end, the passage appears to turn off towards the west-north-west, suggesting there may be more to its plan than what currently remains accessible. The monument is protected under a preservation order dating from 1943.