These are the physical remnants of charcoal production, an industry that left its mark on this valley in the form of levelled, slightly raised or cut terraces, each one the working surface where a carefully stacked mound of timber would have been covered with earth or turf and set to smoulder slowly, converting wood into the high-carbon fuel that smelting and metalworking demanded.

Around seventy-five of these platforms have been recorded on the northern and southern sides of the Upper Lake and to the west and south-west of Reefert Church, one of the small Romanesque ruins within the Glendalough monastic complex. Each platform measures roughly nine metres by six metres, oval in outline, and they appear at irregular intervals across the terrain. A further forty similar platforms were also noted in related surveys, the figures drawn from work by Ua Riain in 1940 and Healy in 1972. The sheer number of them points to sustained industrial activity rather than occasional or opportunistic burning. Glendalough's valley, with its steep oakwood hillsides and proximity to the early medieval monastic settlement, would have provided both the raw material and the demand, since metalworking of various kinds was practised within such communities.