They are easy to overlook, these low, flattened terraces, each roughly nine metres long and six metres wide. But their shape and spacing tell a quiet industrial story, one that has little to do with saints or pilgrims.

These are the remains of a charcoal-making operation, the kind that once supplied fuel to iron smelters and forge works throughout upland Ireland. The process involved stacking coppiced wood into a carefully constructed mound on a level platform, covering it with turf or earth to restrict airflow, and allowing it to smoulder slowly for days. The resulting charcoal burned far hotter than raw timber, making it essential for metalworking before coke became widely available. The platforms, known as hearths or pitsteads, had to be levelled into hillsides by hand, which is why they survive so visibly in the landscape. At Glendalough, more than seventy such platforms have been recorded, spread across the northern and southern sides of the Upper Lake as well as west and south-west of Reefert Church. The two principal observations of the site, by Ua Riain in 1940 and Healy in 1972, counted slightly different totals, suggesting the platforms may have been easier or harder to distinguish depending on vegetation cover at the time of survey.

The concentration of so many platforms in a single valley indicates this was a sustained, organised industry rather than occasional local production. Glendalough's steep, well-wooded slopes would have provided a reliable supply of timber, and the valley's historical associations with ecclesiastical settlement and later landlord estates suggest the charcoal operation could have served either monastic or post-medieval ironworking interests, though the precise period of activity is not firmly established. What remains is a faint but legible trace of an industrial landscape running parallel to, and largely overshadowed by, the famous ruins nearby.