It is a lime kiln, the kind of industrial remnant that was once as common to the Irish countryside as field walls or hawthorn hedges, yet is now largely passed without notice. What survives at Ballyduane is a front wall of random-rubble masonry, meaning stone laid without regular courses or dressing, pierced by a stone-arched recess. That recess is the draw hole, the opening through which the burned lime was raked out once the firing was complete.

Lime kilns were the quiet engines of agricultural improvement across Ireland from the seventeenth century onwards. Farmers burned limestone at high temperatures to produce quicklime, which was then spread on acidic soils to neutralise them and raise crop yields. The process was slow and fuel-hungry, typically requiring several days of continuous firing. The kilns themselves followed a broadly consistent design: a bowl or pot at the top where the limestone and fuel were loaded, and a draw hole at the base, often set into a bank or hillside to allow easy access from below. The positioning of this example against the river bank at Ballyduane is typical of that logic, using the natural slope of the ground to make the structure functional as well as sturdy.