These are the remnants of a charcoal-making industry, and there are more than a hundred of them in this valley, arranged at irregular intervals on the northern and southern shores of the Upper Lake and to the west and south-west of Reefert Church.

Charcoal production relied on carefully stacked and smouldering timber, managed over days to drive off moisture and volatile compounds while leaving behind the dense, high-carbon fuel that iron-working and other industries required. The platforms, each measuring roughly nine metres by six metres, are where the charcoal hearths, or pitsteads, once sat. The wood would have been piled into a domed mound over a central flue, covered with turf or earth to restrict airflow, and then slowly burned. When the process was complete, the collapsed remains left a characteristic flattened, slightly scorched oval in the ground. At Glendalough, at least seventy-five such features were noted on the northern and southern sides of the Upper Lake, with a further forty recorded nearby, all broadly similar in form and scale. The earliest published reference to them appears to be from Ua Riain in 1940, with Healy noting the additional platforms in 1972.

The platforms are distributed across terrain that would once have been well-wooded, close to both the raw material and the monastic and later settlements that generated demand for fuel. Their proximity to Reefert Church, one of the older ecclesiastical structures within the Glendalough complex, raises questions about when exactly this industry was active and who it served, though the surviving record does not yet answer those questions with any precision.