They are not foundations, not burial features, not terraced cultivation plots. They are the physical remains of charcoal production, each one representing a carefully levelled hearth where timber was stacked, covered with turf or earth, and slowly burned over days to produce the dense, clean-burning fuel that industrial and domestic life once depended on.

Seventy-five of these platforms have been recorded on the northern and southern sides of the Upper Lake, and a further forty in the area west and south-west of Reefert Church, one of the early medieval monastic buildings that survive at Glendalough. Each platform measures roughly nine metres by six metres, oval in shape, and they appear at irregular intervals across the terrain rather than in any neat arrangement. The irregularity is itself informative; charcoal-makers, known historically as colliers, chose their spots according to the available timber and the slope of the ground, levelling a shelf just large enough to construct and tend a hearth. The platforms were documented as early as 1940 by Ua Riain, and recorded again by Healy in 1972, but they remain one of the less discussed features of a valley more famous for its round towers and monastic enclosures.

The platforms are spread across the wooded hillsides in an area that walkers pass through regularly, though the features themselves blend into the ground and require a degree of attention to pick out. The association with Reefert Church places at least part of this activity in the vicinity of the monastic site, though the precise period of production is not established from the available record. What is clear is that the scale, more than a hundred platforms across a relatively contained area, points to something systematic rather than occasional, an organised industry rather than a seasonal sideline.