This is a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland, typically Bronze Age in origin. The method involved heating stones in a fire until they were intensely hot, then dropping them into a water-filled trough to bring it to the boil. Over repeated use, the cracked and spent stones were discarded to the side, building up the characteristic horseshoe-shaped mound that survives today.

At Carrowcastle, the mound measures roughly 11 metres north to south and 15 metres east to west, rising to between 0.6 and 0.8 metres in height. It sits on the northern bank of a canalised stream or drain, about 1.6 metres wide and half a metre deep, which meets a low-lying hollow of wet ground some 30 metres to the east. That proximity to water is entirely typical; fulachtaí fia are almost always found near reliable water sources. A gap of about 4 metres separates the main body of the mound from a smaller rise to the east, and this break may mark the original location of the cooking trough, though it could equally reflect later disturbance. The southern edge of the mound has been worn away where farm animals cross the stream at that point. What makes the site quietly more interesting is that a second fulacht fia lies only about 20 metres to the west, suggesting that this particular stretch of ground, with its accessible water and low-lying surroundings, was returned to repeatedly, or used simultaneously, by people going about the business of large-scale food preparation thousands of years ago.