A souterrain, the term for an artificially constructed underground passage or chamber typically associated with early medieval settlement in Ireland, this one is unusual for the complexity of its layout: at least three chambers, a smaller subsidiary chamber off to one side, and a plan that bent and doubled back across a run of at least eleven metres. Most souterrains are relatively straightforward in form; a Z-shaped arrangement of this kind suggests something rather more deliberate in its design, whether for storage, refuge, or concealment.

The souterrain sits within a ringfort, the circular enclosure that was the dominant farmstead type of early medieval Ireland, defined by one or more earthen banks and ditches. The relationship between ringforts and souterrains is well established; the underground passages are frequently found within them, and are thought to have served as cold stores or as places of retreat in times of danger. What makes the Lissananny example more than a footnote is that it was recorded in some detail by Costello in 1903, when enough of the structure survived to produce a measured plan. That plan, published in the early twentieth century, is now the primary evidence for what was once underground here, since the monument has since become inaccessible and the collapse has continued. Today, the only visible trace is a series of linear hollows running east to west across the ground surface, the subsidence marking where the roof of the passage gave way.