Locals have long called it Sunday's Well, and one piece of folklore collected from Malahide schoolchildren offers a memorably matter-of-fact reason why: the well simply was not there on a certain Saturday night, and was first seen the following Sunday morning. The same spring has also been known as St. Sylvester's Well, and a modern plaque at its base gives a foundation date of around AD 430, with a restoration in 2001.

The well's history is tangled in a way that historians have found worth arguing over. Writing in 1838, John D'Alton described a well in the middle of the town covered by an arched enclosure, dedicated to the Blessed Virgin and formerly housing her statue. By 1910, however, M. O'Reilly was pushing back firmly. O'Reilly located the well at the top of New Street, a side street running north from the main street towards the shore, and argued that D'Alton had been misled by circumstantial details: a patron, or pattern day, a traditional gathering at a holy well on a saint's feast, had been held there on Lady Day in August, a Marian feast, and a statue of the Virgin had indeed once stood there. But neither the name nor the dedication properly belonged to Mary; they belonged, O'Reilly argued, to St. Sylvester, as the dedication of the local Catholic church confirmed. O'Reilly also recalled seeing the well in the 1860s, when it was covered by a small circular stone structure, roughly twelve feet high and nine feet wide, with a slate roof and a locked door, and a flight of steps descending inside to the water. By his time of writing, it had already been covered over, the spring redirected to supply a pump at the rear of the National Schools.

The well now sits in a small square behind St. Sylvester's Roman Catholic Church, no longer in the roadway where O'Reilly placed it but still accessible. The original stepped descent into the spring survives, sheltered under a conical stone superstructure. The pattern day associated with the well falls on the 15th of August, and visiting around that date gives the site its most active context, though the well can be visited at other times without difficulty. The steps down to the spring are worth examining closely, as is the plaque at the base, which neatly collapses the site's long disputed identity into a single inscription.