It is classified as a sweathouse, a type of early Irish structure used rather like a sauna, where a fire was lit inside, the embers raked out, and bathers crowded in to sweat through ailments, but there is a problem with this one. The interior walls show no trace of burning or soot, which is precisely the evidence one would expect if fire had ever been set inside. That absence quietly undermines the classification and leaves the building's actual purpose open.

The structure itself is well preserved. It is vaulted and roughly circular, with an internal diameter of just over two metres, walls around two-thirds of a metre thick, and a low doorway facing north-northeast, tall enough to enter with a slight stoop. What makes the situation more complicated still is its position: it is built directly into the south-western face of the enclosing fosse of a ringfort, a fosse being the defensive ditch that runs around the perimeter of such an earthwork. The bank of a conjoined enclosure runs across the top of the building, suggesting the two features were constructed together. Despite this apparent integration with the ringfort earthworks, the structure is thought to date only to the nineteenth century, and may have been built in connection with Merton Hall, a big house shown on the Ordnance Survey six-inch map in the vicinity. Whether it served the estate as a storage building, a shelter, or something else entirely, nobody has yet settled the question.