The opening, roughly two and a half metres wide and the same in height, tapers steadily as it goes back, the walls and roof converging until the whole thing pinches out at ground level about two and a half metres in. It is not a natural feature. This is a primitive copper mine, worked directly into the rock face at around 80 metres above sea level, in ground that today serves as rough boggy pasture for cattle.

The signs of past extraction are still legible if you know what to look for. To the left of the entrance, copper mineralisation stains the rock face and colours a scatter of loose boulders at ground level with the blue-green tinge that indicates copper-bearing ore. About eight metres downslope, a spoil heap of blue-grey sandstone, some of it threaded with quartz veins, covers a roughly four-by-four-metre patch of ground. That patch is almost bare of plants, except for a crust of stereocaulon, a lichen that tolerates the metal-enriched conditions that most vegetation cannot, and whose presence on old mine spoil is itself a kind of residual record of industrial activity. A second worked rock surface sits on the far side of the outcrop, facing north over Derrynane Harbour, though no copper mineralisation survives there. Loose flagstone steps connect this area down to a low drystone wall, and the relatively level ground nearby may have been shaped by the workings themselves. The site was identified as a copper mine by Aoibheann Lambe in 2018, running along a ridge of outcrop that extends some 190 metres in a north-east to south-west direction across the hillside.