Yet the well on the Milverton Demesne near Skerries, Co. Dublin, answers to at least two names, belongs to two entirely different traditions, and contains a hollow stone set into its northern wall whose water, according to local belief, reliably refills itself no matter how many sceptics attempt to empty it. The water is also said to cure sore eyes. On one of the large stones overhanging the well, handprints are visible in the rock; tradition holds that the stone was hurled there from the town of Lusk by Fionn Mac Cumhail himself, which would make it a considerable throw.

Locally the well is known interchangeably as St Mauvee's Well and Fionn's Well, the latter name generally shortened by residents to that form. St Mauvee is St Mobhi, a sixth-century monastic founder whose church is thought to have been established here around 600 AD. The ruined medieval church and its associated graveyard lie roughly fifty yards from the well, and geophysical survey work carried out in 2003 confirmed that both sit within a broader ecclesiastical enclosure, the kind of defined boundary that once marked out early Christian monastic settlements. Inset into the northern wall of the well is a bullaun, a term for a stone with a deliberately hollowed basin, often found at early Christian sites and frequently associated with healing. Folklore collected from Milverton School and preserved in the National Folklore Collection records the legend of a ploughman who refused to stop working on St Mobhi's feast day and was swallowed, along with his horses, into the earth. A road was later cut directly through the cemetery, leaving part of it on the opposite side.

The well is reached via a footpath from the gate lodge at Milverton Hall, near Margaretstown crossroads, approximately three miles west of Skerries. Steps descend from the east into the grotto, and the cairn structure overhead, measuring six metres long and one and a half metres high, gives the space an enclosed, sheltered quality that is immediately apparent on arrival. The hollow stone set into the wall sits roughly four feet above the water level of the well itself; this is the feature worth looking for, distinct from the well water below it. Photographs taken by the folklorist Caoimhín Ó Danachair, now held in the National Folklore Collection at UCD, give a sense of how the site appeared in an earlier era and repay a look before visiting.