This is Tobar Cholmcille, a holy well dedicated to Saint Colmcille, and its position below the high-water mark sets it apart from the vast majority of sacred wells in Ireland, which tend to occupy dry ground near paths, field boundaries, or the edges of settlements. Here, the sea itself is part of the equation.

The well sits on the eastern coast of the island, roughly a hundred metres south of a coastal inlet known as Crompán na Teorann, and it takes the form of a natural round pothole rather than any constructed or improved basin. Holy wells in Ireland are typically springs or pools venerated over centuries, often associated with early Christian saints and visited for purposes of healing or prayer. The attribution to Colmcille, the sixth-century monk who founded the monastery on Iona and remains one of the most widely commemorated saints in the Irish-speaking west, suggests a layer of devotion stretching back a considerable time, even if the precise history of this particular site has not been documented in detail. The local name, Tobar Cholmcille, preserves that dedication in Irish.