It is barely tall enough to crouch in, roughly a metre and a half wide at its widest point, and extends only a few metres before waterlogged rubble closes the way forward. Yet what makes this cramped passage remarkable is its age: it is one of thirty-one prehistoric copper mines that together form the Mount Gabriel mining complex, one of the most significant concentrations of Bronze Age mining in the whole of Europe.

When surveyors drained and examined this particular working in 1984, they found the interior partially choked with rubble infill, and lying on the surface of that infill were stone mauls, the rounded hammerstones that Bronze Age miners used to break ore-bearing rock from the face. The smooth, concave profile of the hanging wall, the ceiling of the working, is itself the product of that same technique: patient, repeated striking rather than any metal tool. The tunnel runs at a bearing of 284 degrees, driven almost horizontally into the rock face. Outside the entrance, a low spoil dump of perhaps three to four metres in diameter records centuries of extracted material, mixed with debris from an adjacent mine just six metres to the south. The site had been noted as far back as 1929 by a Geological Survey of Ireland geologist named Duffy, and again by Jackson in 1968, before William O'Brien's detailed work in the 1980s and 1990s established the full archaeological significance of the complex, published in his monograph on Bronze Age mining at Mount Gabriel.