These are the remnants of charcoal production, an industrial process that once transformed the landscape here in ways that sit oddly alongside the site's reputation for early Christian contemplation.

Charcoal-making platforms, sometimes called pitstead hearths, were created by clearing and levelling a roughly oval area of ground where timber could be carefully stacked, covered with turf and earth, and slowly burned in a low-oxygen environment to produce the dense fuel that ironworking and smelting demanded. At Glendalough, researchers identified as many as 75 such platforms, each measuring approximately nine metres by six metres, distributed at irregular intervals along the northern and southern shores of the Upper Lake and to the west and south-west of Reefert Church. A separate count noted around 40 platforms of a similar character. The sites were recorded by Ua Riain in 1940 and later by Healy in 1972, suggesting the platforms had been recognised as significant long before the landscape around the lakes received closer archaeological attention. The proximity of so many platforms to Reefert Church, a small Romanesque ruin associated with the kings of Leinster, raises questions about the relationship between the monastic settlement and what must have been a fairly intensive local industry.

The platforms are subtle features and easy to miss even when you know what you are looking for. The area around the Upper Lake and Reefert Church is accessible on foot from the main Glendalough visitor centre, and the terrain, particularly on the southern and western sides of the lake, is where the greatest concentration of these earthworks appears to have been recorded.