What emerged was a fulacht fia, a type of site found in great numbers across Ireland, typically consisting of a mound of fire-cracked stones accumulated beside a water-filled trough. The stones would be heated in a fire and dropped into the trough to bring the water to a boil, a method used repeatedly over time until the spent, shattered stones built up into the characteristic low mound. This one, at Belleek on the edge of a waterlogged area with rising ground to the south and west, is a fairly modest example, but its excavation produced details that reward a closer look.

The mound itself measured roughly 8.2 metres east to west and 4 metres north to south, standing only about 26 centimetres high by the time it was investigated. It was composed of heat-shattered sandstone and limestone fragments packed into black soil laced with charcoal, the residue of many fires. Beneath the mound lay the trough, a carefully constructed pit nearly 2.75 metres long with vertical sides and a flat base, most likely originally lined with wood or stone to hold water. Two postholes near the trough suggest some kind of structure once stood over or beside it, perhaps a simple shelter or frame. A small oval pit of unclear purpose sat about 2.5 metres to the south, just outside the mound's edge. The mound had been levelled at some point before excavation, and modern agricultural drainage had disturbed its northern end, meaning the site had quietly absorbed centuries of interference before it was formally recorded under excavation licence 98E0284 by King in 1998. Adding a further layer of interest, a second fulacht fia was found just 20 metres to the northwest and was also excavated, suggesting that this waterlogged corner of Mayo was a repeatedly chosen location, presumably because of reliable access to water and fuel over a long stretch of prehistory.