A souterrain, to use the proper term, is an artificial underground structure, typically built during the early medieval period in Ireland, consisting of one or more chambers connected by low crawlways and constructed from dry-stone walling or natural rock. They are found across Ireland in considerable numbers, often associated with nearby settlement sites, and theories about their purpose range from food storage and refuge to places of concealment during times of raid or conflict. The one at Garraunard is recorded as a surviving monument, which is itself notable; many souterrains have collapsed or been disturbed over the centuries by agricultural activity, drainage works, or simple neglect.

Beyond its classification and location, the specifics of this particular souterrain, its dimensions, its condition, the details of its construction, and any associated finds or nearby features, are not yet in the public domain. What can be said is that Mayo has a reasonable concentration of these structures, generally dating from roughly the sixth to the twelfth centuries, and that their presence in any townland is usually a quiet signal that the surrounding landscape was once more intensively settled than it might appear today. The name Garraunard itself is anglicised from the Irish, and like many Mayo townland names carries geographical or descriptive meaning that connects the place to its long agricultural past.