It is only six metres across, defined by a low ring of stones, with two tall portal stones framing an entrance to the north. But the evidence found beneath and within the walls tells a more industrial story. This was, in all likelihood, a place for smelting iron.

When O Cuileanáin excavated the site in 1955, the finds were unusually specific: iron slag, furnace linings, tuyeres (the nozzles used to direct a forced air blast into a furnace), and a stone implement. The structure itself was carefully built, with walls of alternating upright stones and dry-stone masonry, a technique in which stones are laid without mortar and rely on their own weight and arrangement for stability. A central posthole suggests there was once a roof of some kind. Most telling is the double flue, an elaborate channel running from a circular hearth outwards and under the wall, designed to draw air through the fire and reach the high temperatures needed to work iron. The combination of that flue design and the recovered metalworking debris led O Cuileanáin to propose the structure functioned as a small iron-smelting workshop rather than a domestic dwelling, though the two uses are not always easy to separate in the archaeological record. The portal stones at the entrance are substantial; the western one stands 2.15 metres tall, the eastern 1.8 metres, which gives the modest enclosure an unexpectedly formal threshold for what might once have been a working forge on a hillside overlooking a coastal lake.