To pass it without knowing what it is would be easy enough; it reads, at first glance, as just another piece of old rubble. But the proportions are deliberate, and the craftsmanship is precise: this is a lime kiln, a structure once as essential to the rural Irish landscape as a well or a boundary wall.

Lime kilns were used to burn limestone at high temperatures, producing quicklime that could be spread on acidic agricultural land to improve its fertility, or mixed with water and sand to make mortar for building. The Derrylahan example is a roadside kiln, constructed directly into a natural slope, which would have made loading it from above considerably easier. Its eastern-facing façade is built from random rubble, meaning irregularly shaped stones laid without a uniform course, and measures roughly 1.7 metres high by 1.5 metres wide. Set into this face is a lintelled recess, a recessed opening spanned by a single flat stone across the top, about 1.45 metres tall and a metre wide, with sloping slabs arranged at the rear. Near the base of this recess is a small rectangular opening, approximately 30 centimetres high and 45 centimetres wide, through which ash and spent material could be raked out once a burn was complete. The whole of the top is now heavily overgrown, vegetation having gradually colonised what was once a working throat through which fuel and stone would have been fed.

These kilns fell out of use as industrially produced lime became available and affordable, leaving hundreds of them scattered across the Irish countryside in varying states of survival. The Derrylahan kiln is modest in scale but complete enough in its essential form to show clearly how the type worked, each element, the recess, the sloping slabs, the small basal ope, serving a specific function in the burning and drawing process.