These structures, found across Ulster and Connacht in particular, were used for therapeutic sweating: a fire would be lit inside, the chamber heated through, the embers cleared out, and the user would crawl in and sweat out whatever ailed them, before plunging into a nearby stream or pool. The one at Ballynashee is now little more than a depression in the earth, roughly 1.5 metres across and 0.8 metres deep, its entrance barely wide enough to admit a person on hands and knees, at just 0.4 metres across and 0.75 metres long.

The structure is lined with rough, unmortared limestone rubble, and local tradition holds that it once had a domed stone roof, which has since collapsed or been removed. It does not appear on the Ordnance Survey six-inch map of 1838, which is itself a useful clue: the map's absence of the site suggests either that it had already fallen out of use by that point, or that it was too modest a feature to be recorded. The site is thought to date to after 1700, placing it in the period when sweathouses were most commonly documented across rural Ireland, before they gradually disappeared as formalised medical care became more accessible. The eastern-facing slope above the river would have made practical sense as a location, with water close at hand for the cooling phase that followed the sweat.

The site today is covered with overgrowth, and its muddy base and tumbled rubble give little indication of what it once was without some prior knowledge of the form. The Camoge River lies just twenty metres to the south, and the surrounding pasture remains wet and rough underfoot, so the approach requires a degree of persistence.