It is a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, and this one has been doing a reasonable job of disappearing back into the ground. The mound stands roughly 0.8 metres high and is heavily overgrown, while the stone-lined trough that once formed its working heart is now a water-filled depression rather than any kind of obvious ancient feature.

Fulachtaí fia, the plural form, are typically Bronze Age in date and consist of a horseshoe-shaped mound of fire-cracked stone beside a water source, with a trough nearby that would have been filled with water and heated using stones thrown from a fire. The Derreenataggart example follows the pattern faithfully, right down to the marshy, waterlogged ground that made such sites practical in the first place. The trough here was dug out around forty years before it was first formally noted by O'Brien in 1970, apparently by local people, which explains why it remains partially exposed even as the surrounding vegetation closes in. The 1992 Archaeological Inventory of County Cork recorded the site in its then-current state, and little seems to have changed in the decades since.