Roughly circular, measuring about ten metres across and less than half a metre high, it would read as a natural rise in the land were it not for the heat-shattered stones visible along its outer edge, particularly on the eroding western side. Those burnt and fractured stones are the giveaway: this is a fulacht fia, a type of prehistoric cooking site found in great numbers across Ireland, typically in low-lying and waterlogged terrain exactly like this.

A fulacht fia works on a simple but effective principle. Stones are heated in a fire and then dropped into a water-filled trough, bringing the water rapidly to a boil. The repeated heating and sudden cooling shatters the stones over time, and it is these cracked, fire-reddened fragments that accumulate around the trough to form the characteristic horseshoe-shaped mound. At Annagh, a slight depression in the south-western quadrant of the mound is thought to mark where the trough once sat. A stream still runs close to the western side, partly choked with sediment, and it seems that material from this stream was at some point deposited into the trough itself, gradually filling it in and giving the mound its unusually rounded, near-circular appearance rather than the open horseshoe more commonly seen at such sites. The upper surface of the mound is noticeably uneven, a further trace of the disturbance and accumulation the site has undergone over the centuries.