A souterrain, the term used for the stone-lined subterranean passages and chambers built by early medieval Irish communities, typically for storage or refuge, this one is now sealed off from the world, its entrance reduced to a narrow opening through which, if you look carefully, the dressed stone lining and flat lintels of the roof are just visible.

When P. J. Hartnett examined the site in 1939 and recorded his findings, the chamber measured six feet by two and a half feet, a space barely wide enough to lie down in. The floor was already covered in debris at that point, which meant the effective height from the rubble to the flagged roof was just three feet. Small even by the standards of its type, this was not a place designed for comfort. Souterrains of this kind are generally associated with ringforts, the circular enclosed farmsteads that were the dominant settlement form in early medieval Ireland, and their function was practical rather than ceremonial, likely used to keep food cool, to shelter people or animals during raids, or both. The association here with the Barrahaurin ringfort fits that pattern precisely.

The chamber is no longer accessible, and what can be seen today is limited to what the small opening permits: a glimpse of stone and lintel in the dark. It is an unassuming thing, easy to overlook, which is perhaps why it remains quietly interesting.