St. Catherine's Well at Saintdoolaghs in north County Dublin is not a spring in a field or a trickle beside a roadside shrine; it is an underground chamber, a rectangular vaulted building enclosing the well itself, lit from the north by a double-light window and roofed in pitched stone. Holy wells in Ireland are common enough, but one that functions essentially as a small subterranean building, with its own gable and architectural intention, is rather less so.

The well sits about thirty metres north of St. Doolagh's Church and joins onto the northern wall of a second well, St. Doolagh's Well, making this a paired sacred site of some density. Folklore gathered in 1937 from Baldoyle Convent, and separately from Kinsealy School, fills in details that the stonework alone cannot supply. The 1937 accounts describe a miraculous origin, with a holy person appearing to a monk and naming the well for St. Catherine, connecting its foundation to the displacement of Catholic communities during the Cromwellian period. One school account notes a crude altar on the south side of the interior, used by priests to celebrate Mass during the Penal Laws, when public Catholic worship was prohibited. The Fagan family, described in the folklore as a very old family, are credited with erecting the well structure, and their name is said to appear on a stone ornament inside. The same accounts mention a cure for sore eyes attributed to the water, a feature shared by many Irish holy wells, and a nearby feature called Saint Patrick's Bed, a low-lying spot in the field that fills with water at certain times of year.

The well is close to the Malahide road, roughly a hundred yards off it according to the school folklore, and convenient to the church and graveyard. Summer is the more practical time to visit the interior, as the water level drops enough to allow access without difficulty; in other seasons it can fill considerably. Once inside, look for the altar recess on the south side and the stone ornament associated with the Fagan family. The double-light window in the north wall provides the only natural light, so the interior remains dim even on a bright day, which gives the space a quality that is less about atmosphere and more about the simple fact of being underground, enclosed, and surprisingly complete.