It measures roughly 14.4 metres north-west to south-east and 12.2 metres east to west, rising no more than 0.7 metres at its highest point. The opening faces west, and at the south-western edge, grey ash and heat-fractured stones are still visible at the surface, the residue of repeated, deliberate burning carried out perhaps three or four thousand years ago.

This is a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland. The standard interpretation holds that such sites were used for boiling water by heating stones in a fire and dropping them into a water-filled trough; the stones crack and shatter with the thermal shock, and the broken fragments accumulate over time into the distinctive mound. The horseshoe or kidney shape is characteristic, with the open end typically positioned near the original trough. What makes the Derry example quietly remarkable is its company. Another fulacht fia lies roughly 50 metres to the north-east, and a further possible example sits about 20 metres to the north. Three of these monuments within such a short distance of one another suggests this particular patch of ground was returned to again and again, possibly over generations, for whatever communal or practical purpose these sites served.