The mound measures twelve metres long and eight metres wide, and local memory records that it once stood around 0.6 metres high before it was levelled, presumably by agricultural activity over the years. What lies beneath the turf is the accumulated debris of a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland and Britain, particularly from the Bronze Age onwards.

A fulacht fia typically consists of a trough, often timber-lined or cut into the ground, beside which a fire was kept burning to heat stones. The stones were dropped into water held in the trough until it reached boiling point, and the cracked, heat-shattered fragments were then raked aside. Over generations of repeated use, these discarded burnt stones built up into the horseshoe-shaped or oval mounds that survive today, sometimes in considerable quantities in a single landscape. Ireland has thousands of recorded examples, making them one of the most common field monuments in the country, though their exact purpose is still debated. Cooking is the most widely accepted explanation, but some researchers have proposed uses ranging from textile processing to bathing. The example at Lyroe sits close to the River Laney, which is entirely typical; fulachta fia are almost always found near a reliable water source.