This is a sweathouse, the Irish equivalent of a sauna, used in rural communities well into the nineteenth century as a treatment for rheumatism and other ailments. A fire would be lit inside, the chamber heated for hours, the embers raked out, and the patient then crawled in and sweated it out on the warm stone floor before plunging into cold water nearby. The structure at Crosshill is notable for having two conjoined chambers rather than one, which is relatively unusual among surviving examples.

The building consists of an eastern rectangular chamber, roughly 1.25 metres by 1.1 metres internally and just a metre high, with a lintelled roof, meaning flat slabs laid horizontally across the top. This connects through a low hatch, only about twenty centimetres high, to a western D-shaped chamber with a corbelled roof, where stones are laid in overlapping courses that curve inward to form a rough dome. Each chamber has its own entrance facing south, both of them requiring a person to crouch or crawl to enter. The whole structure is built into the hillside scarp rather than standing freely, which would have helped retain heat. A deserted farmstead lies just to the west, a reminder that this was once a working agricultural landscape rather than an isolated curiosity. The site appears on the 1914 edition of the Ordnance Survey six-inch map, and another sweathouse survives roughly 240 metres to the north-east, suggesting this corner of Roscommon once had a cluster of these structures serving the local community.