A souterrain is an underground passage constructed in the early medieval period, typically built from unmortared stone and used for storage, refuge, or both. This one was incorporated into the south-western section of the enclosing bank of a rath, the circular earthen ringfort beside which it lies, so that the defensive boundary of the settlement and the hidden passage beneath it were, in a sense, the same structure.

What survives today is fragmentary. The passage was built using drystone construction, meaning the walls were laid without mortar, relying entirely on the careful placement of stone. It runs roughly north-east to south-west and is approximately one metre wide, though its full length can no longer be determined. Almost the entire structure has collapsed, and only a single roof lintel remains in place. The most telling detail is a small recess that extends northwards from the north-west side-wall, just inside a breach at the north-eastern end. Recesses of this kind are occasionally found in Irish souterrains and may have served as hiding places or storage alcoves within an already concealed space. That this one survives, even partially legible, within an otherwise ruined passage makes it the most informative remnant of the site.