The structure at Seltannaveeny is a compact, circular room, just 1.6 metres across and 1.65 metres high, with slightly inclined drystone walls and a lintelled roof. A sweathouse typically worked by heating the interior with burning turf, raking out the embers, and then allowing a person to sit inside the retained heat, sweating out whatever ailment had brought them there. The entrance here is barely half a metre wide and half a metre tall, meaning anyone using it would have had to crawl inside, which also helped to trap the heat.

The structure sits pressed into a steep west-facing slope beside a stream, and it is surrounded, at a distance of roughly 150 metres in three directions, by the remains of deserted houses. That arrangement is quietly telling. Sweathouses tended to be communal resources, used by the households of a townland rather than belonging to any single family, and the cluster of abandoned settlements around this one fits that pattern well. The site appears on the 1914 edition of the Ordnance Survey six-inch map, though the sweathouse itself is almost certainly considerably older than that date of cartographic recognition; the 1914 map simply happens to be the earliest surviving record to mark it. The drystone construction, without mortar, relies entirely on the careful placement of stone against stone, and the fact that the chamber still stands to its original height suggests the builder knew exactly what they were doing.