Each one measures roughly nine metres by six metres, 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 remnants of charcoal production, an industrial process that would once have transformed this wooded valley into a smoky, carefully managed workplace. Charcoal-making platforms, sometimes called hearths or pitsteads, were created by levelling a patch of ground on a slope, stacking cut wood into a dome-shaped pile, covering it with earth or turf, and burning it slowly over several days to drive off moisture and produce dense, carbon-rich charcoal. The flat oval shape is the characteristic signature left behind.

The scale here is striking. At least 75 such platforms have been recorded in the area around the Upper Lake, with a further 40 of the same type noted in a separate count. The site was documented by Ua Riain in 1940 and subsequently noted by Healy in 1972, suggesting the platforms had been recognised as a coherent industrial landscape for some decades before any formal survey. Glendalough had the raw materials that charcoal production required, namely extensive woodland and, critically, a ready market in the form of early metalworking. The monastic settlement at Glendalough, one of the most significant in early medieval Ireland, would have needed charcoal for metalwork, and later ironworking operations in the Wicklow valleys continued to consume large quantities of locally produced fuel well into the post-medieval period. The precise period of use for these particular platforms is not firmly established from what has been recorded, but the number and distribution suggest sustained, organised production rather than occasional opportunistic burning.