On its upper face, three small circular hollows have been deliberately pecked into the rock, each no more than five centimetres across and two centimetres deep. These are cupmarks, among the most enigmatic of all prehistoric carvings found in Ireland and Britain. Simple as they appear, nobody is entirely certain what they meant to the people who made them, or when, though they are generally associated with the Bronze Age. Their presence here, on an almost unremarkable piece of ground on an east-facing slope, is a reminder that the Irish landscape is scattered with quiet evidence of lives lived thousands of years ago.

The slab itself is earth-fast, meaning it is set firmly into the ground rather than free-standing, and measures roughly 2.6 metres east to west and 2.2 metres north to south, with its northeast corner rising about 30 centimetres above the surrounding soil. It is a substantial piece of stone, though you might walk past it without a second glance were it not for those three small depressions on its surface. Cupmarks occur across Ireland and throughout Atlantic Europe, often on outcrops, boulders, and standing stones, sometimes alone and sometimes in elaborate groupings. The Arduslough example is modest by comparison with more complex carved sites, but that modesty is perhaps part of what makes it worth attention.