It measures roughly twenty metres across at its widest point, and to a casual observer it might read as nothing more than an overgrown hump of rock rising from the water. But beneath the undergrowth lies a considerable quantity of stone, the collapsed remains of what was once a deliberate human construction.

This is a crannog, a type of artificial or semi-artificial island dwelling used in Ireland and Scotland from the Bronze Age through to the early modern period, sometimes built up with layers of timber, peat, and stone to create a defensible or simply practical home in shallow water. The site at Loch Céim na Caillí caught the attention of a visitor named Layard, who noted in 1897 that the island was "plainly an old stone dwelling" and that the walls, though badly broken down, could still be traced. By the time the cartographer and writer Tim Robinson surveyed the area in 1985, the site had become fully overgrown, though he recorded a possible landing place on the eastern side, suggesting the island was once approached by boat from that direction. The lake's name, Céim na Caillí, meaning something close to "the step" or "pass of the old woman", adds a layer of local character without illuminating the crannog's specific history, which remains largely unknown.