One piece in particular has quietly moved house over the centuries. A cross-slab, measuring 1.6 metres tall by 0.6 metres wide, was originally located at Reefert Church, one of the smaller ruined churches on the south bank of the upper lake, and has since been moved for safekeeping to St Kevin's Church within the main monastic enclosure.

What makes the carving itself worth attention is its design. The cross is formed from a single continuous interlaced band, looping at each end without ever breaking, and gathering into a circular knot at the centre. This kind of knotwork, in which one unbroken line generates the entire pattern, carries obvious symbolic weight in early medieval Christian carving, suggesting eternity or divine completeness. The whole composition sits within a framed border, giving it a considered, finished quality. Harold Leask, the architectural historian who catalogued a great deal of early Irish ecclesiastical stonework in the mid-twentieth century, noted the slab in his 1950 study and recorded that it once stood roughly 12 metres to the west of Reefert Church. Robert Cochrane had drawn and documented it even earlier, in material published in a 1925 report on the ecclesiastical remains at Glendalough that drew on a Commissioners of Public Works survey from 1911 to 1912, meaning the slab has been attracting scholarly attention for well over a century.