That hollow in the earth is, in all likelihood, the roof of something that has given way. The leading interpretation is that it marks a partially collapsed souterrain, one of those stone-lined underground passages or chambers that early medieval communities built beneath and beside their settlements, used variously for storage, refuge, or both.

The souterrain sits within a conjoined ringfort, a type of enclosure in which two or more roughly circular earthwork compounds share a boundary, suggesting a settlement of some complexity and probably some duration. The Ballinrobe and District Archaeological Survey, compiled by D. Lavelle and published in 1994 by the Lough Mask and Lough Carra Tourist Development Association, recorded the feature and noted its dimensions, though even at that point it was inaccessible. The depression itself is the only visible evidence of what lies beneath, and the qualification in the record, that it "may represent" a souterrain, is honest: without excavation, the underground form and extent of any surviving passage or chamber cannot be confirmed.