The one at Gortglass in County Kerry is a quiet example of a site type that has puzzled archaeologists for generations. A fulacht fia typically survives as a low, horseshoe-shaped mound of fire-cracked stone and dark, charcoal-stained earth, usually found close to a source of water. The mound is the accumulated debris from repeated use of a trough, most likely a timber- or stone-lined pit filled with water, into which heated stones were dropped to bring the liquid to a boil. What exactly this process was used for is still debated, with cooking, brewing, bathing, and textile processing all put forward as possibilities over the years.

Most fulachtaí fia date to the Bronze Age, roughly 1500 to 500 BC, though some sites show evidence of use across longer periods. The Kerry landscape contains a notable concentration of them, partly owing to the county's wet, low-lying ground, which would have provided the reliable water sources these sites required. Gortglass, as a placename, derives from the Irish gort glas, meaning green field or green garden plot, a modest, agricultural name that gives little away about the prehistoric activity recorded there.