They are, in fact, the physical remains of an industrial process, charcoal production, that once operated at considerable scale in this valley. Charcoal-making platforms, sometimes called hearths or pitsteads, were levelled areas cut into hillsides where cordwood was stacked, covered with earth and turf, and slowly burned over several days to produce the dense carbon fuel that iron-smelting and other crafts demanded.

Somewhere in the region of seventy-five of these platforms have been recorded on the northern and southern shores of the Upper Lake, each roughly nine metres by six metres in size and arranged at irregular intervals rather than in any planned grid. A further forty similar platforms were noted separately, suggesting the site was revisited or expanded over time, or simply that different surveys captured different portions of the same broad industrial zone. The references go back at least to 1940, when Ua Riain documented the features, with Healy adding further detail in 1972. The sheer number of platforms points to sustained, organised production rather than casual or occasional burning, though the precise period of operation and the industry it served remain matters for further investigation.

The platforms are concentrated near Reefert Church, one of the early medieval ecclesiastical remains for which Glendalough is known, and around the Upper Lake shore. Walking the paths in that part of the valley, a careful eye at ground level will pick out the characteristic flattened oval terraces cut into the slope, sometimes still edged by a low lip of soil where the platform was shaped. They are unassuming features, but their repetition across the hillside gives some sense of how busy and purposeful this landscape once was.