A souterrain is a man-made underground structure, typically associated with early medieval settlements in Ireland, and generally thought to have served as a place of refuge, storage, or concealment. This one adds a further curiosity immediately outside its entrance: a roughly semi-circular walled enclosure, about two metres across and 1.3 metres high, its unmortared limestone rubble curving gently inward at the top and sealed beneath a single large limestone capstone measuring roughly 1.7 square metres and 0.4 metres thick. The function of this antechamber-like space is not recorded, but its careful construction in dry-stone rubble suggests it was no afterthought.

The souterrain sits within the bank of a cashel, which is a type of stone-walled enclosure, broadly equivalent to a ringfort but built from stone rather than earth, typically associated with early medieval farmsteads in Ireland. The lintelled entrance to the passage itself is notably low, only 0.3 metres high and 1.1 metres wide, set at the base of the south-western wall of the antechamber. From there the passage runs east-west for 1.7 metres before being stopped by collapsed stonework. The limestone rubble lining the passage walls is also unmortared, consistent with the dry-stone construction visible throughout. Whether the passage originally extended further behind that blockage remains an open question.