Locals call it 'the furnace', and two competing traditions have grown up around it: one holds that it was a lime kiln where seashells were burned to produce agricultural lime, a practice once common along the west coast of Ireland; the other that it was an iron smelter, drawing on bog-iron, the nodules of iron oxide that accumulate naturally in waterlogged ground, and using the surrounding peat as fuel. The building appears on the Ordnance Survey six-inch maps of both 1838 and 1921, placing it firmly in the 18th or 19th century, but its precise purpose remains unresolved.

What survives is a three-room stone structure, originally T-shaped in plan, with a fourth room to the east now largely collapsed. The western side of the building is set directly against rising ground, which would have given workers easy access to the roof and to a chimney, now ruined. The roofing of the western and southern rooms is particularly notable: rather than timber, the builders used corbelling, a technique in which stone slabs are laid in slightly overlapping horizontal courses, each projecting a little further inward than the one below, until the gap is closed at the top with a row of heavy lintels. It is a method more often associated with prehistoric monuments than with industrial buildings, and its use here suggests either a shortage of timber or considerable confidence in working with stone. At the junction of the western and southern rooms sits the furnace itself, a square chamber two metres across with clear scorching on its inner walls. Nearby, a small circular hole in one of the ceiling lintels may have been a socket for machinery gearing, and a low stone plinth against the south wall of the western room was almost certainly a base for some kind of equipment. Outside, a channel nearly one and a half metres wide runs along the north wall and extends westward for 28 metres into a large crescent-shaped depression that may once have served as a millpond or water reservoir, suggesting the operation was more mechanised than its remote setting might imply.