A souterrain, to use the technical term, is a man-made underground structure, typically built during the early medieval period in Ireland, usually consisting of one or more corbelled or dry-stone chambers connected by low crawlways. They appear throughout the Irish landscape, sometimes beneath the sites of ringforts, and their precise function has long been debated, with theories ranging from food storage and refuge to ceremonial use. The one at Kilmore is recorded as a monument, quietly occupying its place in the archaeological map of Mayo.

Beyond its classification and location, the specific details of this particular souterrain remain sparse. What can be said generally is that Mayo contains a significant concentration of early medieval activity, and souterrains in the region tend to be associated with the farming communities that built and occupied ringforts, the circular enclosed settlements that defined the rural landscape of Ireland from roughly the sixth to the twelfth centuries. The underground chambers would have offered a cool, stable environment suited to storing dairy produce and other perishables, and their narrow, defensible entrances may have served as places of concealment during times of conflict. Whether this example retains its structural integrity, how many chambers it contains, or what its current condition might be, is not something the available record speaks to.