It measures just 3.6 metres across and rises to about 1.65 metres, modest enough to be dismissed as a natural feature or a field clearance heap. But it is classified as a sweathouse, one of a scattered tradition of small Irish structures that functioned as a form of communal steam bath, heated by burning fuel inside until the interior was intensely hot, then raked clear so that a person could crouch within and sweat out ailments.

Sweathouses, known in Irish as tigh alluis, are found across Ulster and parts of Connacht in particular, and most date to the post-medieval period. The Magheralackagh example is tentatively placed after 1700 AD. Typically they were built into hillsides or banks to retain heat, with a low entrance just large enough to crawl through, and their use was associated with the treatment of rheumatism and other complaints. The surviving form here, a conical mound of earth and stone adjacent to a field boundary on a sloping pasture, is consistent with that tradition, though the interior structure, if any survives, is not described in detail.