A souterrain, to use the archaeological term, is an artificial underground structure, typically built during the early medieval period in Ireland, constructed from dry-stone walling and roofed with large flat slabs. They were associated with nearby settlements and served various purposes, among them food storage, refuge, or as concealed escape routes from enclosures under threat. The fact that one exists at Keeloges New places this quiet corner of Mayo within a network of early medieval activity that extended across the whole island, though most of these structures remain little known beyond the immediate locality.

The specific details of this particular souterrain, its dimensions, its condition, the circumstances of its discovery, and any associated finds or features, are not yet a matter of public record. What can be said is that souterrains in the west of Ireland were typically constructed between roughly the seventh and twelfth centuries, often in connection with ringforts or other enclosed farmsteads. Mayo has a notable concentration of such monuments, a reflection of how densely settled the western seaboard was during the early Christian period, before later centuries of upheaval and land clearance obscured so much of what had been built.