What once sat here was a fulacht fia, the term used for a type of prehistoric cooking site found in extraordinary numbers across Ireland, typically consisting of a horseshoe-shaped mound of fire-cracked stone beside a trough and a water source. The burnt stone accumulates over time as rocks are heated in a fire and dropped into a water-filled trough to bring it to the boil. At Rathmorrissy, the mound and the pond together tell a coherent prehistoric story, though the mound itself has largely been erased.

When Cody recorded the site in 1989, it was already in poor shape, described as an ill-defined, partly grass-covered mound of burnt stone, oval in plan and measuring roughly 7 metres north to south by 4 metres east to west, rising just half a metre above the surrounding ground. Livestock drinking at the adjacent pond were actively eroding it. By the time an inspection was carried out in 1984, the monument had been almost completely levelled. Only a low, subrectangular spread of burnt stone remained, measuring 7.2 metres by 3.9 metres and standing just 0.25 metres high, partially covered by sod. What makes the location more than just a footnote is its context: two further fulachta fia lie within roughly 100 metres, one approximately 95 metres to the northwest and another about 45 metres to the southwest. The clustering of these sites suggests that this stretch of wet, low-lying ground was returned to repeatedly, which is a pattern seen elsewhere in Ireland where marshy terrain provided reliable water sources close to higher ground.