This is a souterrain, a type of roofed underground structure built during the early medieval period, typically used for storage, refuge, or both. What makes this particular example quietly remarkable is not its dimensions, though at a minimum of eight metres long and less than a metre and a half wide it is a tight, deliberate space, but the tradition attached to it. Local folklore holds that this cramped stone tunnel was once the forge of Lon Mac Loimhtha, the mythological smith of the Tuatha Dé Danann, the supernatural race whose exploits run through the oldest layers of Irish mythology.

The souterrain runs on a roughly north-north-east to south-south-west axis, and near its northern end the roof survives intact over a stretch of about 2.6 metres, with four large capstone lintels still in place. When the antiquarian T. J. Westropp measured those lintels in 1896, he recorded them at six feet, or roughly 1.83 metres, in length. A displaced lintel also covers the rounded northern terminal of the passage, where loose stones lie scattered across the floor. The southern half of the passage has given itself over to nettles. The folkloric identification of the site as a forge appeared in the Ordnance Survey Letters of 1839, a remarkable nineteenth-century collection of local knowledge gathered by surveyors travelling the country, and Westropp returned to the same tradition in a paper on the Cow Legend of Corofin published in the Journal of the Royal Society of Antiquaries of Ireland in 1895. The association of a real, physical underground space with a divine craftsman is a small example of how mythological geography rooted itself in specific, touchable places rather than remaining purely abstract.