Behind that low opening, partly choked by spoil tipped from the surrounding waste dumps, a chamber opens out to roughly six metres in length and up to four metres across, its rubble floor wet near the back wall where water pools in the dark. It is not a dramatic void so much as a compressed, intimate space, cut into the base of a conspicuous east-facing rock scarp, and it gives almost nothing away from the outside.

Mount Gabriel is well known to archaeologists because its slopes hold some of the earliest evidence of copper mining in Ireland or Britain, with workings dated to the Bronze Age, roughly the second millennium BC. This particular working, catalogued by William O'Brien in 1987 as mine 9, sits about eighty-four metres north of a cluster of associated mines on the same hillside. The technique used at sites like this involved fire-setting, where heat was applied to rock faces to fracture the stone, followed by the use of stone hammers to extract the copper ore. The scale of the Mount Gabriel workings as a group points to organised, repeated extraction over a long period, not opportunistic digging, which makes each individual chamber, however modest in dimension, part of a much larger prehistoric undertaking. The mine holds a preservation order under the National Monuments Acts, a reminder that what looks like a hole in a hillside is, in legal and archaeological terms, a scheduled monument.