The chamber at its core measures barely 1.42 metres across and stands only 0.8 metres high, yet it was built with considerable care: dry stone walls corbelled inward to form a domed roof, and a narrow lintelled passage, less than half a metre wide, leading into the interior from the south-east. This is a sweathouse, a type of small stone structure used in Ireland as a form of therapeutic steam bath, in which a fire would be lit inside to heat the walls, the ashes raked out, and the user crawling in to sweat in the retained warmth. They are found across Ireland, particularly in the north and west, and are generally thought to have been used to treat rheumatic complaints and other ailments.

The Ballyourane example sits within a sub-rectangular mound roughly 3.6 metres by 4 metres, and was recorded on the Ordnance Survey six-inch map of 1842, where it appears as a rectangular structure, its true form not yet apparent from above ground. A second passage runs parallel to the first on the north-west side of the mound, though its interior has collapsed. The proximity to Ballyourane Castle raises questions about who used it and when, though no documentary record connects the two directly. Sweathouses are notoriously difficult to date with precision; they continued in use in rural Ireland into the nineteenth century, long after their origins, which some scholars place in the medieval period or earlier.

The structure is small enough to be easily overlooked, sitting quietly within its earthen mound. The collapsed second passage hints that the site may have been more elaborate than what survives today, or simply that it saw enough sustained use to eventually give way.