Beyond that gap lies a souterrain, an underground passage of the kind built throughout early medieval Ireland, typically as a place of refuge or storage attached to a settlement. This one sits within a rath, a circular earthwork enclosure that would once have defined a farmstead, probably dating to somewhere between the sixth and twelfth centuries. The ground has subsided across a roughly two-and-a-half-metre stretch in the southern half of the rath interior, and it is at the lowest point of that collapse that the entrance becomes visible.

The passage itself is constructed in drystone, meaning the walls are built from carefully stacked uncut stone without mortar, and it is roofed with large flat lintels laid horizontally across the top. The interior width runs to approximately two metres, which is reasonably generous for a structure of this type. Souterrains vary considerably in scale and complexity across Ireland, from simple single chambers to branching networks of passages, but the defining characteristic is always the same: constructed underground, out of sight, and built to last. The presence of a rath nearby is consistent with the broader pattern, since souterrains are almost always found in association with these enclosed farmsteads rather than in isolation.