The one at Boyogonnell in County Mayo is a quiet example of this widespread but still somewhat enigmatic type of site. A fulacht fia, at its most basic, is a burnt mound, typically a horseshoe-shaped heap of fire-cracked stone and dark, charred earth left behind by repeated episodes of heating water, most likely for cooking, though bathing, brewing, and textile processing have all been proposed over the years. They cluster near water sources, boggy ground, or stream banks, and the Mayo landscape, with its abundance of wet, low-lying terrain, is well suited to them.

Most fulachtaí fia date to the Bronze Age, broadly between 1800 and 800 BC, though some sites show earlier or later activity. The method was straightforward in principle: stones were heated in a fire and then dropped into a water-filled trough, usually timber-lined, bringing the water to a boil without direct contact with flame. The mound itself is the accumulated debris of this process, stones that had cracked and become useless discarded again and again over what may have been centuries of intermittent use. The site at Boyogonnell takes its name from the surrounding townland, a unit of land division ancient in itself, and its presence there suggests the area supported human activity during prehistory, even if the precise details of its use and condition on the ground remain to be fully documented.