That detail alone sets them apart from the vast majority of Ireland's holy wells, which tend to occupy sheltered inland spots, spring-fed and permanent. Here, the sacred and the tidal are the same thing.

Both wells are natural formations in the coastal rock rather than constructed features. The first, roughly 170 metres south-west of a nearby graveyard, is a large smooth basin hollowed into the outer flank of a rock outcrop, triangular in shape, its surface worn to a bowl by water and time. The second lies closer to the low-water mark, about 270 metres south of the same graveyard, and takes the form of a smooth pothole approximately a metre in diameter. Deep inside a cleft within it, coins have been left by visitors, offerings pressed into a crack in the rock rather than simply tossed into water. The detail was recorded by the cartographer and writer Tim Robinson, whose meticulous documentation of the Connemara landscape captured much that would otherwise have gone unnoted. St Columcille, also known as Columba, was the sixth-century monk credited with founding the monastery on Iona, and his cult spread widely across Ireland and Scotland, attaching itself to springs, rocks, and coastal features far beyond any place he is likely to have visited in person.

Because both wells lie below the high-water mark, any visit depends on the tides. The coin-filled pothole, being closer to the low-water mark, would be accessible only during a reasonably low tide, and the coins lodged in its cleft suggest that people have been making the effort for some time.