It is a sweathouse, a type of Irish vernacular sauna used for centuries to treat rheumatism, skin complaints, and general ailments. The method was straightforward: a fire was lit inside the low stone chamber, the embers were raked out, the patient crawled in, and the residual heat did its work. This example at Briscloonagh is notable partly for what it is missing. Most sweathouses are set into or covered by an earthen mound, which helped retain heat; this one has been rebuilt without one, leaving it unusually exposed and readable as a structure.

The site was recorded, without description, on the Ordnance Survey six-inch map of 1835, which suggests it was already a known feature of the landscape at that point, even if the surveyors did not consider it worth annotating. By the 1910 edition of the same map, it appears simply as "Sweat Ho.", and two houses are marked roughly 150 and 200 metres to the north-east, implying the structure was still legible, if not necessarily still in active use, within living memory of that survey. The rebuilt chamber is compact: an internal diameter of 1.35 metres, a height of 1.85 metres, a paved floor, and a west-facing entrance just 0.55 metres wide and 0.71 metres high, low enough that anyone entering would have had to stoop or crawl. That entrance size was deliberate, designed to minimise heat loss once the chamber was sealed.