It is a sweathouse, a type of structure once used across rural Ireland as a form of folk medicine, functioning much like a sauna. A fire would be lit inside, the chamber allowed to heat thoroughly, the embers raked out, and a person crawling in through the low entrance would sweat out fevers, rheumatism, or other complaints. The entrance here, at the north-east, has collapsed entirely, and the interior diameter of the chamber measures just 1.45 metres, enough for a person to crouch or lie, but little more.

What makes this particular site quietly telling is its cartographic history. It appears on the 1914 edition of the Ordnance Survey six-inch map, but not, it seems, on earlier editions, which raises questions about when it was formally recorded rather than simply used. Around it, the landscape carries its own weight of absence: deserted houses lie roughly 100 metres to the north-west and south-west. Whether the sweathouse and the abandonment of those houses are connected in time is not recorded, but the proximity gives the site a particular atmosphere, a cluster of structures that once served a community whose daily life has otherwise left very little trace at Greaghnaglogh.