It is a souterrain, one of the dry-stone or rock-cut tunnels that early medieval Irish communities constructed beneath or beside their settlements, most commonly between roughly the sixth and twelfth centuries. Their precise purposes are still debated; cool storage for dairy produce, refuge in times of raid, or some combination of both are the explanations most often advanced. What makes the Ardhoom example quietly notable is simply how little is publicly known about it. It exists as a name, a map reference, and a classification, which is itself a kind of archaeological condition: presence confirmed, detail withheld.

Souterrains are found across Ireland in considerable numbers, and Mayo has its share, often associated with ringforts, the circular earthen or stone enclosures that were the standard farmstead form of the early medieval period. The underground chambers typically consist of one or more passages, sometimes with side chambers or creeps, narrow constrictions deliberately built to slow an intruder. Construction could involve corbelled stonework, timber lintels, or combinations of both, depending on local materials and the preferences of whoever commissioned the work. Without more specific information about the Ardhoom site, whether it retains its original form, how it was discovered, or what if anything was found within it, the structure remains at the edge of the knowable.