That alone makes it worth pausing over. Most souterrains, the dry-laid stone tunnels built beneath early medieval settlements in Ireland, run in a single direction, used variously for storage, refuge, or ventilation. This one does something more elaborate, bending from one axis to another through a low connecting passage known as a creep.

The structure is twin-chambered and built entirely of drystone, meaning the walls and roof are assembled without mortar, relying on carefully fitted stones to hold their shape. The first chamber runs roughly north to south and extends to 8.8 metres in length; a creep then connects it to a second chamber, shorter at 5.75 metres, which runs east to west. The overall effect is an L-shaped underground complex sitting within the rath, the circular earthwork enclosure that would once have defined a farmstead or minor settlement above ground. Two openings exist, one in the fosse, the external ditch of the ringfort, at the south-east, and another near the eastern end of the second chamber. Both are considered probably modern breaches rather than original entrances, which suggests the souterrain's ancient access points remain a matter of some uncertainty. Despite this, the structure itself is described as well-preserved, a notable condition for a stone-lined underground passage that has been in the ground for roughly a thousand years or more.