The structure is a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically associated with the ringforts, or raths, that dot the Irish landscape. These subterranean features served various purposes, from cold storage to refuge, and their presence within a rath is not unusual; but the condition of this particular example rewards a closer look.

The chamber itself is drystone-built, meaning constructed without mortar, relying instead on carefully placed stones to hold their form, and extends more than 4.4 metres along a north-east to south-west axis. What makes this souterrain worth attention is the feature at its south-western end: a hollow running more than 6 metres in length, with traces of drystone walling still visible along its edges, which cuts directly through the bank of the surrounding rath. Archaeologists working from the published inventory of North Galway interpret this as a robbed-out section, a length of the original passage whose stone was removed at some point, leaving only the depression and fragmentary walling as evidence of what once continued further. It is a small detail, but it speaks to centuries of activity around the site, people returning not to use the souterrain but to dismantle it, taking the dressed stone for other purposes. Access to the surviving chamber is now possible through modern breaches at both ends, gaps that were not part of the original design but have since become the practical means of entry.