They are not natural. Each one, roughly nine metres by six, is what remains of a charcoal-burning hearth, where timber would have been stacked into a mound, covered with earth or turf to restrict airflow, and slowly combusted over several days to produce the dense, hot-burning charcoal required for metalworking and smelting.

In total, researchers have identified as many as seventy-five such platforms on the northern and southern sides of the Upper Lake alone, with a further forty recorded in similar form elsewhere in the area. The sites were noted by Ua Riain as early as 1940, and later by Healy in 1972, though they remain relatively obscure compared to the ecclesiastical ruins that draw most visitors to Glendalough. The sheer number of platforms suggests industrial-scale production at some point in the valley's history, pointing to a level of organised manufacturing activity that sits alongside, rather than apart from, the monastic settlement the area is better known for. Early Irish monasteries were frequently centres of craft production, and the proximity of these platforms to Reefert Church hints at a connection, though the precise period of their use has not been firmly established from the available evidence.