These are the remains of charcoal-making platforms, sometimes called hearths or pitsteads, where woodland fuel was converted into charcoal through slow, controlled burning. The process involved stacking coppiced timber into a carefully shaped mound, covering it with turf or earth to restrict airflow, and then tending the smouldering heap for days at a time. The platforms were levelled into the hillside to keep the mound stable, and their distinctive oval shape, roughly nine metres by six metres, is what makes them identifiable centuries later.

Around seventy-five such platforms have been recorded on the northern and southern sides of the Upper Lake and to the west and south-west of Reefert Church, one of the early medieval ecclesiastical buildings within the wider Glendalough monastic complex. A further forty similar platforms were noted in the same general area. The concentration of so many platforms in a single valley points to an industrial scale of production at some point in the past, most likely connected to iron-smelting or metalworking activity, which required large and consistent quantities of charcoal as fuel. Glendalough and the surrounding Wicklow uplands had both the raw material, in the form of managed woodland, and the streams and ore deposits that would have supported such industry, though the precise period of most intensive use at this site remains uncertain from what survives.