It is a souterrain, a type of structure built during the early medieval period in Ireland, typically consisting of one or more dry-stone tunnels or chambers dug into the earth or constructed below ground level and then covered over. Their precise purposes are still debated among archaeologists, with theories ranging from food storage and refuge to ritual use, though the mundane explanation of cool, stable storage space has considerable support. What makes the Toorard example quietly notable is less any dramatic feature of the site itself and more the simple fact of its existence: Mayo has a reasonable concentration of these structures, most of them modest, most of them unvisited.

Souterrains were generally constructed between roughly the seventh and twelfth centuries and are often found in association with ringforts, the circular enclosed settlements that were the dominant farmstead type of early medieval Ireland. The underground passages would have been accessible from within the enclosure, offering concealment or storage that was effectively invisible from outside. Beyond its classification and location, the specific details of the Toorard souterrain, its dimensions, construction method, current condition, and precise relationship to any above-ground features nearby, remain unavailable in the public record at present.