A souterrain, the term used for a man-made underground passage or chamber typically associated with early medieval settlement in Ireland, once lay within a ringfort here. By 1937, all three of its chambers had collapsed inward, and today there is no visible surface trace of either the souterrain or, apparently, its enclosing earthwork.

The only contemporary description comes from a 1937 account by someone recorded simply as Broker, who noted the underground rooms and their condition at that time. The structure sat inside a ringfort, one of the thousands of circular enclosed farmsteads that dot the Irish countryside and date broadly to the early medieval period, roughly 500 to 1000 AD. Souterrains were commonly built within or adjacent to such enclosures, though their precise function is still debated; they may have served as cool storage for dairy produce, as places of refuge, or both. The example at Dooneens appears to have been a modest one by any measure, three chambers being a fairly typical configuration, and it was already lost to subsidence within living memory of the twentieth century.

What makes this site quietly interesting is precisely its absence. There is nothing to see, no earthen bank, no lintel stone, no hollow in the ground pointing to what lies below. The ringfort that once enclosed the souterrain has itself left no visible trace. It survives in the record, documented in a single sentence from a survey carried out nearly ninety years ago, as a place that existed and is now, for all practical purposes, gone.