They are the physical remains of charcoal production, each platform representing a carefully levelled working surface where timber was stacked, covered with earth and turf, and burned slowly in controlled conditions to produce the dense, carbon-rich fuel that iron-smelting and metalworking once depended upon.

At least 75 of these platforms have been recorded on the northern and southern sides of the Upper Lake, as well as to the west and south-west of Reefert Church, one of the valley's Romanesque stone churches. Each measures roughly 9 metres by 6 metres, a size consistent with the circular or oval clearings, sometimes called hearths or pitsteads, that charcoal-makers, or colliers, would have prepared on sloping ground to keep the burn even. A further 40 comparable platforms were noted separately, suggesting the industry was extensive rather than incidental. The distribution around Reefert Church and the Upper Lake points to a concentrated area of woodland management and fuel production, though the precise period of activity is not firmly established in the available documentation. The sites were noted by Ua Riain in 1940 and later by Healy in 1972, indicating awareness of them among local historians well before any formal survey.

The platforms are most legible when the ground vegetation is low, typically in late autumn or winter, when the slight terracing of each oval becomes visible against the hillside. They lie within the Glendalough valley, which is part of Wicklow Mountains National Park, and can be approached on foot along the paths that run beside the Upper Lake toward Reefert Church. The platforms do not announce themselves; they require a slow pace and a willingness to look at the ground rather than the skyline.