Men, women, and children performed what contemporary observers called "superstitious ceremonies", drank the water, and returned home to spend nine days recounting the miraculous effects. A late sixteenth-century account noted, with barely concealed scepticism, that the water was "generally reported to be very hot" and that its holiness peaked precisely on St Patrick's Day, "or else the inhabitants of Dublin are more foolish upon that day than they be all the year after". The well in question, known as the southern well of St Patrick, fontem Sancti Patricii in Latin, lies today within the Provost's garden of Trinity College Dublin, just west of the college's Nassau Street entrance. The street itself preserves the memory of it: Nassau Street was formerly called St Patrick's Well Lane, or Sráid Thobar Phádraig in Irish.

The well's history is considerably older than the pilgrimages suggest. A deed of 1592, drawn up when the City of Dublin transferred the grounds of the dissolved monastery of All Hallows to the newly founded Trinity College, used the spring as a fixed point marking the southern boundary of the property. That places it at the edge of monastic and then collegiate geography for centuries. Writing in 1610, Barnaby Rich described the same annual scene at the well, and in 1612 Patrick Playne, a Trinity student, challenged his colleagues to explain away the sheer numbers of people gathering there if they truly found no virtue in the water. The Primate of Armagh is recorded as having attended and drunk from it. The well's prominence was not merely devotional; later commentators noted that Dublin Corporation had anciently paid a form of tribute to the Bishop of Armagh in connection with its use. The ceremonies appear to have faded after the Reformation, and when the spring dried up around 1728 or 1729, the event was notable enough to inspire a poem by Jonathan Swift. Dublin Corporation attempted, apparently without much success, to restore the water supply to the south side of the city in 1731. By 1756, the antiquarian Dr Rutty, who made considerable efforts to document Dublin's ancient wells, could find no trace of it at all, and knew it only by hearsay.

The well that is visible today in the Provost's garden is not easily accessible to the general public, as the garden is private college grounds. The question of which surviving spring, if any, is the original southern well remains genuinely unresolved. Writing in 1860, Clibborn concluded that the well behind No. 9 Nassau Street, close to a lane connecting Nassau Street to Frederick Lane South, had the strongest claim. A spring behind No. 15 Nassau Street was still being named St Patrick's Well in leases from Simpson's Hospital, with the right to draw from it retained as a valued privilege. The old Ordnance Survey maps, both the 1837 six-inch edition and the 1863 twenty-five-inch edition, mark the well's location, and these remain useful for anyone trying to orient themselves to where the spring once served an entire city's thirst.