There are scores of them, distributed at irregular intervals along the northern and southern sides of the Upper Lake and to the west and south-west of the early medieval Reefert Church. Each platform measures roughly nine metres by six metres. They are the remnants of charcoal production, and they represent an industrial past that is almost entirely invisible to most visitors who pass through this celebrated monastic valley.

Charcoal-making platforms of this kind, sometimes called hearth platforms or pitstead platforms, were created by levelling ground on a hillside to provide a flat, stable surface on which timber could be carefully stacked and slowly burned in low-oxygen conditions to produce charcoal. The process was labour-intensive and required skilled management to prevent the wood from combusting fully. The charcoal produced was essential fuel for iron smelting and metalworking. At Lugduff, over seventy such platforms were identified and described by Ua Riain in 1940, with a further forty noted by Healy in 1972, suggesting that the site was substantial in scale and likely operated over an extended period. The proximity of so many platforms to Reefert Church raises quiet questions about the relationship between the monastic settlement at Glendalough and the industrial activity on its doorstep, though the notes do not provide dates precise enough to pin the charcoal-making to any particular phase of the monastery's history.