These are the physical remains of charcoal production, an industrial process that involved stacking and slowly burning wood under a covering of earth and turf to drive off moisture and volatile compounds, leaving behind the dense carbon fuel that smelters and metalworkers depended upon. The platforms, each roughly nine metres by six, are what surveyors call hearths or pitsteads, the flattened or slightly scooped ground where charcoal burners built and tended their slow fires.

Researchers identified around seventy-five of these platforms on the northern and southern shores of the Upper Lake and to the west and south-west of Reefert Church, one of the early medieval monastic buildings for which the Glendalough valley is known. A separate survey recorded approximately forty similar platforms in the same general area. The precise period of use is not firmly established from the available evidence, but charcoal production of this kind was associated across Ireland and Britain with ironworking industries that could span the early medieval period right through to the post-medieval centuries. The sheer number of platforms suggests sustained, repeated use of these hillsides as a working fuel-producing landscape rather than any casual or occasional activity.

Visitors walking the forest paths around the Upper Lake, particularly those heading towards Reefert Church, are moving through what was once a quietly industrial zone. The platforms are subtle features and most walkers pass them without a second glance, but once you know what to look for, the gentle oval levelling of the ground, often on a slope where a flat surface would not otherwise occur naturally, becomes surprisingly legible.