Built from random rubble sandstone, it is a substantial industrial ruin, and an easy thing to walk past without quite registering what it once was: a working iron smelter, roaring with heat, in the middle of what is now one of Ireland's most visited lakeside landscapes.

The furnace probably dates to the second half of the seventeenth century, and its presence at Muckross is a consequence of an earlier failure elsewhere. Sir William Petty, the political economist and surveyor who accumulated vast landholdings in Kerry following the Cromwellian settlement, operated an ironworks at Glanaroughty. When that operation closed in the 1670s, the cause was a familiar one for the period: the surrounding woodland had been stripped to feed the furnaces, and there was no longer enough timber to produce the charcoal on which smelting depended. Petty's operations relocated to Muckross, where sufficient woodland remained. The furnace that survives there reflects the technology of the time in some detail. A semicircular casting arch, 1.7 metres high and 4 metres wide, sits centrally in the northeast face. A smaller flat-headed bellows arch, partially buried in rubble, would have admitted the blast of air needed to drive combustion, and a tuyere hole, formed by two inwardly angled stones, survives in situ within it. A tuyere is the nozzle or opening through which forced air enters a furnace, and its survival here is a rare piece of functional detail. Putlog holes above the casting arch, used to anchor timber scaffolding or structural supports, suggest a gangway once ran from a sloping earthen embankment ten metres to the east, allowing workers to charge the furnace from above. A flying buttress reinforces the southwest wall, and a vaulted recess opens inward toward the rear of the casting arch.