Each one measures roughly nine metres by six, and they appear at irregular intervals along 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 shaped this valley as surely as any of its more celebrated ruins.

Charcoal-making platforms, sometimes called hearths or pitsteads, were level areas cut or built into a slope to hold a stack of timber that would be slowly burned under a covering of turf and earth, a process requiring days of careful tending to convert green wood into the dense, smokeless fuel demanded by iron-smelting and metalworking. Seventy-five of these platforms were recorded on both sides of the Upper Lake, with a further forty of a similar character noted separately, suggesting sustained and organised production over a considerable period. Ua Riain documented the site in 1940, and later work by Healy in 1972 confirmed and extended the count. The proximity to Reefert Church, one of the early medieval ecclesiastical buildings within the Glendalough complex, raises questions about the relationship between the monastic community and industrial activity in the valley, though the precise dating of the platforms remains uncertain.