A souterrain is an underground passage built from drystone, that is, stones laid without mortar, typically constructed during the early medieval period as a place of refuge, cool storage, or concealment. This one is L-shaped in plan, with a total recorded length of more than 18.2 metres, and despite its much-collapsed state it retains a legible geometry: the longer arm runs north to south at 9.3 metres, while a shorter arm of 8.9 metres branches off from the south-east end and runs east to west.

The rath it sits within was a type of enclosed farmstead common across early medieval Ireland, typically defined by one or more earthen banks and ditches. Placing a souterrain inside the western sector of such an enclosure was not unusual; builders often positioned these underground structures close to a dwelling, allowing quick access from above. The passage here is just over 1.4 metres wide along its main axis, narrow enough to make movement awkward and defensive in character. Whether it once held food stores, sheltered people during raids, or served some other purpose is not recorded, but the care taken in its construction, even in its ruined state, suggests it mattered to whoever built it.