The structure is a souterrain, a type of artificial underground chamber or tunnel built during the early medieval period, typically from drystone masonry, and associated with ringforts and cashels across Ireland. Their purposes are debated; storage, refuge, and ventilation for adjacent structures have all been proposed. This particular example is partially collapsed and formally inaccessible, which gives it an quietly paradoxical quality: a hidden space that is more hidden now than its builders ever intended.

The souterrain is L-shaped in plan, with its long axis running northwest to southeast before turning to run roughly north-northeast to south-southwest at its southeastern end. It measures more than 19.7 metres in length and around 1.6 metres in width, making it a reasonably substantial construction. It sits inside a cashel, the term used for a stone-walled ringfort, the remains of which are recorded separately. The site appears in McCaffrey's 1952 survey of Galway antiquities, suggesting it has been known to researchers for decades, though the collapse of the drystone lining has rendered any closer investigation impossible without significant intervention.