A souterrain, to give it its proper name, is a man-made underground passage or chamber, typically constructed during the early medieval period in Ireland and often associated with nearby settlement sites. What makes this particular example unusual is not just its concealment but the fact that it was found, partially recorded, and then effectively lost again, leaving two inscribed ogham stones still in situ underground.

The story unfolds in two visits separated by roughly two decades. In 1872, the antiquarian Brash recorded a possible long cist burial and a single ogham stone from the townland. Ogham is an early medieval script in which letters are represented by a series of notches and lines cut along the edge of a stone, most commonly found in the south of Ireland and used primarily to record personal names. Then in 1896, a man named Quarry came to Monataggart with a more commercial purpose: to buy that ogham stone for the Royal Irish Academy. While he was there, he persuaded the landowner to dig further, hoping to uncover additional inscribed stones. The excavation revealed a separate stone-lined chamber measuring approximately eighteen feet in length, five feet wide, and five feet deep, with wood ashes at one end and what appeared to be a small flue. Two of the upright stones forming the walls carried ogham inscriptions. The presence of the flue is what nudges scholars towards identifying the structure as a souterrain rather than a burial context, though certainty remains elusive.

The site today leaves no visible surface trace. The ogham stone purchased by Quarry was removed, but those two inscribed uprights remain where they were found, sealed underground in a chamber that has not, as far as the record shows, been opened since 1896.