Each one measures roughly nine metres by six, and they appear at irregular intervals on the northern and southern sides of the lake and to the west and south-west of Reefert Church. They are the physical remains of charcoal production, an industry that once occupied this woodland at a significant scale.

Charcoal-making platforms, sometimes called hearths or pitsteads, were levelled into hillsides to create a flat working surface where timber could be carefully stacked and covered with earth or turf, then slowly combusted over several days with minimal oxygen. The resulting charcoal was dense, high in carbon, and essential for smelting and smithing. The platforms at Lugduff number at least seventy-five, with a further forty of similar character recorded in the same general area, suggesting sustained industrial use of this valley rather than occasional or incidental burning. Ua Riain noted these features as early as 1940, and later work by Healy in 1972 confirmed and extended the count. Glendalough is most associated today with its monastic settlement, and Reefert Church, a small Romanesque ruin on the lakeshore, is one of its quieter corners. The concentration of platforms around that church and along both shores of the Upper Lake places this industrial activity right alongside the ecclesiastical one, a reminder that early medieval and later communities here were as concerned with fuel and metalwork as with prayer.