It never appeared on any edition of the Ordnance Survey six-inch maps, meaning it escaped the notice of generations of cartographers, and it was absent from the first systematic monument record compiled in 1989. It only entered the official record in 1995. For a structure that once served a practical, even central, role in the agricultural economy of its area, it has managed to remain remarkably invisible.

What survives is a lime kiln, a type of structure once common across rural Ireland. Farmers and landowners used them to burn limestone at high temperatures, producing quicklime that could be spread on acidic soils to improve fertility, or used in building mortars and whitewash. The Mahanagh example measures roughly 4.6 metres east to west and 4.4 metres north to south, standing to about 1.6 metres in height. It is built into a west-facing slope, a typical arrangement that allowed the kiln to be loaded with fuel and stone from the higher ground at the rear while the finished lime was drawn from a recess at the front. That recess, on the western side, is 1.35 metres wide, though its top and front face have collapsed. Behind it, sloping slabs channel towards a narrow opening at the base, and the circular funnel above, around 1.3 metres in diameter, is still lined with stones that have been visibly shattered by repeated intense heat. The kiln is thought to date to after 1700, placing it within the period of improving agriculture that saw these structures spread across the Irish countryside.