It is not a stone-lined shaft or a sheltered pool but a shallow, bowl-shaped hollow worn into the sloping face of a prominent rock, barely twenty centimetres across. That such a modest natural feature should carry the weight of devotion is, in itself, a quietly telling thing about how sacred geography works along this stretch of the Connemara coast.

The well is associated with St Macdara, one of the more compelling figures in the early Irish monastic tradition, whose own island, Oileán Mhac Dara, is visible from this spot looking south across the water. That sight line feels deliberate, or at least it has been read that way over generations. St Macdara's island holds a small oratory of exceptional antiquity, and the saint was venerated especially by fishermen of the region, who were said to dip their sails in salute when passing the island. Whether the hollow in the rock at Inishlackan was always understood in relation to that visible shrine, or whether the association accumulated over time, is not recorded, but the two places are clearly bound together in local religious geography.

The well sits at the southern tip of the island, on the foreshore itself, which means the approach and the experience of it are shaped by tide and weather. At low water, the rock on which it sits is accessible and the hollow may hold rainwater or residual seawater; at high tide, the site is submerged or close to it. Looking south from that spot, with Macdara's island on the horizon, gives some sense of why this particular rock, on this particular edge of land, came to be regarded as something other than ordinary.