These are ancient burnt mound sites, typically Bronze Age in date, consisting of a horseshoe-shaped mound of fire-cracked stone and charcoal built up beside a trough, usually timber-lined, which was filled with water and heated by dropping stones from a fire directly into it. Thousands of them survive across Ireland, yet what they were actually used for remains genuinely contested. Cooking is the most widely accepted explanation, demonstrated through practical experiment, but brewing, bathing, and industrial processing have all been proposed with varying degrees of seriousness.

The presence of one at Granny places it within a wider pattern of Bronze Age activity across the Kilkenny landscape, where river margins, boggy ground, and accessible water sources seem to have drawn repeated use over centuries. Fulachtaí fia, to use the Irish plural, tend to cluster near wet ground precisely because the whole process depended on a reliable water supply. The mounds themselves are the accumulated debris of many firings, the rejected stone that cracked and shattered with thermal shock and was simply raked aside after each use. That slow accumulation is what makes them visible today, sometimes as low earthen swellings in pasture, sometimes only identified during development or drainage work.