This is a sweathouse, a type of structure once found across Ireland that functioned as a rudimentary sauna. A fire would be lit inside, the chamber heated, and the user would crawl in to sweat out illness or pain, emerging to plunge into cold water nearby. Here, the stream immediately to the north, which broadens and deepens a little further west, almost certainly served exactly that purpose as a plunge pool, making the pairing of structure and water source part of the original design rather than coincidence.

The chamber itself is carefully built, constructed from sandstone with quartz pebble inclusions. It measures roughly 2.2 metres north to south and 1.55 metres east to west on the interior, with a maximum internal height of just over 1.5 metres, enough to crouch but not to stand. The walling was likely drystone originally, though clay has since filtered down between the stones. At the rear, the boulders were corbelled gradually inward to form a roof, a technique where stones are laid in progressively overhanging courses until they meet overhead; this roof has largely collapsed, and only a single lintel survives at the back of the chamber. The entrance, just half a metre wide, opens to the north through roughly hewn jamb stones, with the side walls continuing a little beyond the entrance before sloping down towards the exterior ground level. The structure was traditionally known as a sweathouse locally and identified as such by a man named Jack Ryan. A comparable example survives about three kilometres to the north-west, in Boolatin townland on the south-western slopes of Keeper Hill itself, suggesting these uplands once supported a small network of such facilities.