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 cut into bedrock. Their exact purposes are still debated among archaeologists, with theories ranging from food storage and refuge to ritual use, though most were associated with nearby settlement sites above ground.

Souterrains are found across Ireland in considerable numbers, particularly in areas of early Christian and pre-Norman rural settlement. Mayo has a strong concentration of early medieval remains, and a souterrain in a townland like Darhanagh would ordinarily point toward the presence of a rath or ringfort in the vicinity, since the two types of monument frequently occur together. Beyond the fact of its existence and location, the specific details of this particular souterrain, its construction, condition, dimensions, and any associated finds, remain unavailable in the public domain at present.