What remains of their activity has been levelled flat, invisible now to any passing eye, but its presence is recorded: a fulacht fia, the term given to a type of prehistoric cooking site found in considerable numbers across Ireland, particularly in low-lying, wet ground close to water sources.

Fulachtaí fia, the plural form, are among the most common archaeological monument types in Ireland, yet they remain genuinely mysterious in certain respects. The typical arrangement involved a trough dug into the ground, lined to hold water, which was then heated by dropping fire-cracked stones into it. The mounds of those shattered, heat-spent stones are what usually survives, forming the characteristic horseshoe shape archaeologists look for in fields and bogs. At Derryduff, that mound no longer stands above the surface; the site has been levelled, most likely through centuries of agricultural activity. The association with a spring is consistent with what is known about these sites more broadly: proximity to a reliable water source was not incidental but essential to whatever was happening there. Whether that was cooking meat, processing hides, or something else entirely is a question that continues to generate debate among archaeologists.