They measure roughly nine metres by six, and there are at least seventy-five of them, arranged at irregular intervals. Most visitors pass through this landscape entirely unaware that these low earthen terraces represent an industrial past, one that predates the more celebrated monastic ruins nearby by many centuries in its continuity of use.

The platforms are the remnants of charcoal production, a process that required carefully levelled ground on which to stack and slowly burn timber under a covering of earth or turf, starving the wood of oxygen to produce the dense, hot-burning fuel that smelting and metalworking depended upon. The technique is ancient, and charcoal-making sites of this kind are often overlooked precisely because they leave so modest a trace. Ua Riain noted the Glendalough platforms as early as 1940, recording their distribution around the Upper Lake, and Healy, writing in 1972, documented a further forty examples of the same oval form in the same area. The sheer number of surviving platforms suggests sustained, organised production over a considerable period, making use of the dense oakwoods that still partly clothe the valley sides.