They are easy to miss, and easier still to misread as natural features of the terrain. In fact they are the physical traces of an industrial process, the production of charcoal, which left its mark on this landscape in the form of roughly seventy-five platforms, each measuring approximately nine metres by six metres, arranged at irregular intervals across the northern and southern sides of the Upper Lake.

Charcoal-making platforms, sometimes called hearths or pitsteads, were created by levelling a section of sloped ground to provide a stable, flat surface on which timber could be stacked, covered with turf or earth, and burned slowly in controlled conditions. The resulting charcoal was a far more efficient fuel than raw wood, and was in demand for iron-smelting, glassmaking, and other industries that required intense, sustained heat. The oval shape and modest dimensions of the Glendalough platforms are characteristic of this kind of woodland industry. Their presence here, noted by Ua Riain in 1940 and later documented by Healy in 1972, suggests sustained and organised woodland exploitation across the valley, not far from one of the most celebrated early medieval monastic sites in Ireland. Reefert Church itself, beside which several of the platforms cluster, is a small Romanesque ruin associated with the kings of Leinster.

The platforms sit within the Glendalough valley in an area now managed as part of a national park, and many are visible along the woodland paths that skirt the Upper Lake. They are subtle rather than dramatic, low earthen shelves on the slope, but once you know what to look for, the sheer number of them begins to convey a sense of how intensively this quiet valley was once put to work.