It is more than eight metres in total length, yet easy to overlook entirely. What it marks is the collapsed roof of a souterrain, an underground passage or chamber built during the early medieval period, typically by cutting trenches into the earth, lining them with stone, and roofing them with large slabs. These structures are found across Ireland and were used variously for storage, refuge, or as escape routes connected to nearby settlements. Here, the ground has long since subsided into the void below, leaving the shape of the passage legible as a sunken outline rather than an opening.

The souterrain sits within the WSW sector of a cashel, a type of stone-walled enclosure that would have enclosed a farmstead or small settlement in early medieval Ireland. The two features almost certainly belong to the same phase of occupation, the souterrain serving whoever lived within the cashel walls. The collapsed passage has two arms: the longer runs roughly east-northeast to west-southwest, measuring 4.7 metres in length and 1.6 metres across, while a shorter arm extends from its south-west end and turns to run south-southeast, measuring 3.4 metres long and 1.7 metres wide. That L-shaped plan is a common configuration in Irish souterrains, where a bent passage offered both structural stability and a degree of concealment for anyone sheltering inside.