These are the remnants of charcoal-making platforms, known as hearths or pitsteads, where timber would have been stacked into carefully constructed mounds, covered with earth and turf to restrict airflow, and slowly burned over several days to produce the dense, hot-burning charcoal essential for smelting and metalworking. There are at least 75 of them on the northern and southern sides of the Upper Lake, as well as a cluster to the west and south-west of Reefert Church, and each one measures roughly nine metres by six metres, levelled into the terrain at irregular intervals across the landscape.

The platforms were recorded by Ua Riain in 1940 and subsequently by Healy in 1972, who noted a further forty comparable examples nearby. Their proximity to Reefert Church and the broader monastic settlement of Glendalough raises questions about who operated this industry and when. Charcoal production at this scale would have demanded a steady supply of coppiced or felled woodland and points to sustained, organised activity rather than occasional or casual burning. The valley's forested hillsides would have provided the raw material, while the monastic community, or industries working in association with it, likely had good reason to produce charcoal for metalworking, given the considerable craft and ecclesiastical metalwork associated with early Irish monasteries. Whether these platforms date to the medieval monastic period or to later ironworking industries in the Wicklow uplands is not firmly established from the available evidence.

The platforms are spread across the terrain rather than clustered in one obvious spot, so those walking the path along the Upper Lake towards Reefert Church may find themselves passing over or alongside several without immediately recognising them for what they are. The slight, levelled terraces are most legible when vegetation is low and the raking light of a winter or early spring day catches the subtle changes in the slope.