In the south Kildare town of Castledermot, a granite stone sits embedded in the ground with a near-perfect circular hole bored through its centre. It is not immediately obvious what it is, and that ambiguity is rather the point. The stone measures roughly 71 centimetres in diameter, with the hole itself spanning about 16 centimetres across, and it has been set so deeply into the earth that whatever base or broader form it may once have had remains out of sight.

The uncertainty around its original purpose is genuine and unresolved. One possibility is that it functioned as a millstone, a workaday object used to grind grain, with the central hole fitted over a spindle to allow rotation. Millstones were commonly made from whatever durable local stone was available, and granite would have served adequately. But the classification has never been settled with confidence, and the stone may have had an entirely different function. It was recorded in 1986 by Bradley and colleagues, who noted its dimensions and material without arriving at a firm conclusion about its origins or use.