They are the remains of a charcoal-making operation, and their sheer number gives some sense of the industrial scale at which fuel was once being produced in this valley.

Charcoal was made by stacking cut wood into a dome-shaped pile, covering it with turf or earth to restrict airflow, and burning it slowly over several days. The process required a flat, level surface, which is why charcoal makers cut and built these platforms, known as hearths or pitsteads, into sloping ground. At Lugduff, the platforms measure roughly nine metres by six metres, a size consistent with a working hearth large enough to produce a meaningful yield. Researchers recorded around 75 such platforms on the northern and southern sides of the Upper Lake, with a further 40 noted to the west and southwest of Reefert Church, the latter a twelfth-century monastic site associated with the early Christian settlement at Glendalough. The platforms were documented by Ua Riain in 1940 and again by Healy in 1972, suggesting they had been visible and noteworthy features of the landscape for some decades before anyone thought to count them formally.

The platforms are distributed across both sides of the valley in no obviously regular pattern, which may reflect the practical logic of working close to available timber rather than any planned layout. Reefert Church, near which a cluster of them sits, takes its name from the Irish meaning "royal burial place", and the proximity of an industrial process to a sacred site is one of those quiet incongruities that the valley quietly accumulates.