The example at Oldcastle in County Cork belongs to this largely unsung category: a structure built not for ceremony or defence, but for the hard agricultural work of producing quicklime, which farmers spread across acidic soils to improve fertility and which builders mixed into mortar. The kilns were typically stone-built, bottle-shaped chambers where layers of limestone and fuel, usually coal or wood, were burned together at high temperatures over many hours. What remained was a caustic, powdery material that was essential to both farming and construction across rural Ireland for centuries.