The structure is a souterrain, a type of underground chamber built in drystone masonry and typically associated with early medieval ringforts, or raths, in Ireland. Their precise purposes are still debated, but souterrains are generally thought to have served as cool storage spaces, places of refuge, or both. This one takes an L-shaped course, which is not unusual for the type, though the combination of partial collapse, an inaccessible creepway, and a second passage that can only be inferred from its lintels protruding at the surface gives it a particular quality of incompleteness.

The accessible portion begins at an opening measuring roughly two metres by three-quarters of a metre, set nine metres west of the inner face of the rath's bank. From there it leads into a passage standing about 1.2 metres high, enough to crouch through but not to walk upright. The south-west side of this passage has been lost to collapse. At the north-east end, a low creepway, a constricted connecting passage often used in souterrains to slow intruders or control airflow, closes off further progress. Beyond it, a second passage appears to continue north-west for approximately 6.7 metres. That second section is known only from a line of stone lintels visible at ground level, their edges still embedded in the earth above. The full extent of the system, and what originally lay at its terminus, remains unknown.