Corn-drying kilns of this type were a practical necessity in Ireland's damp climate, used to dry harvested grain before it could be milled or stored. The keyhole shape is characteristic, comprising a bowl where the grain sat above the heat, connected to a long flue through which the fire was fed from one end.

The kiln at Fermoy was cut into the natural incline of the slope, with the bowl measuring roughly one and a half metres across and just under two thirds of a metre deep. The flue ran two and a half metres downslope to the south, and the whole structure was lined with angular, largely unworked stones. Among those stones, excavator O'Connell identified something telling: at least one, and possibly two, fragments of rotary quernstones, the circular hand-grinding stones used to process grain into flour, had been repurposed as lining material. A further quern fragment turned up in a pit some fifteen metres to the west. These were not prestigious objects, but their presence suggests a working agricultural site where milling and drying went hand in hand, and where old or broken equipment was simply folded back into the fabric of the place. The charred plant remains recovered from the bowl were identified mainly as oats, and charcoal from the same deposit has been radiocarbon dated to between 1270 and 1400 AD, placing the kiln firmly in the later medieval period. A cluster of stake-holes was also recorded to the west of the kiln, though no clear structure could be read from them.