These oval terraces, each measuring roughly nine metres by six, are not the remains of buildings or burial mounds but the workings of a charcoal industry, pressed into the hillsides at irregular intervals on the northern and southern shores of the Upper Lake and to the west and south-west of Reefert Church.

Charcoal-making platforms of this kind, sometimes called hearth platforms or pitstead platforms, were created by cutting and levelling a shelf into a slope to provide a flat, stable surface on which a timber stack could be built and slowly burned under a covering of turf or soil. The controlled smothering produced charcoal rather than ash, a fuel dense enough for smelting and smithing. At Glendalough, at least seventy-five such platforms have been recorded in one cluster alone, with a further forty noted separately, suggesting an operation of considerable scale rather than occasional, opportunistic burning. The presence of so many platforms in the vicinity of the early medieval monastic site raises questions that are not easily resolved. Whether the industry dates to the monastic period itself, when ironworking was well attested at such settlements, or to a later era of more commercial woodland exploitation, is difficult to say without more detailed investigation. The sites were noted by Ua Riain in 1940 and subsequently by Healy in 1972, and the sheer number of platforms recorded across both surveys points to an industry that shaped this landscape as much as any church or round tower.