The well is dedicated to St. Nessan, a figure associated with early Irish monasticism, and the island itself has a long ecclesiastical history, with the remains of a medieval church still visible there. What makes this spring quietly unusual is the paper trail it left: in 1757, at a time when Irish mineral waters were being catalogued with the same empirical enthusiasm being applied to spa waters across Europe, this remote tidal island made the list.

The record comes from Dr. John Rutty, a Dublin Quaker physician who published his exhaustive survey, "The Mineral Waters of Ireland", in 1757. Rutty tested samples from springs across the country, assessing their chemical properties at a moment when the therapeutic value of natural waters was considered a serious branch of medicine rather than fringe practice. St. Nessan's spring on Ireland's Eye appears in his survey under Table 1 EE, which places it among waters he considered worth examining. The spring was later marked on the Ordnance Survey Ireland 25-inch map edition of 1863, meaning it was still recognised as a discrete, nameable feature more than a century after Rutty's visit.

Ireland's Eye is accessible by a short boat trip from Howth, with seasonal ferry services running during the warmer months. The island is managed as a nature reserve, and landing is straightforward at the small beach on the eastern side. The medieval church ruin, known as the Church of St. Nessan, sits near the landing point and is the most obvious landmark once ashore. The holy well itself is a less conspicuous feature, and visitors hoping to locate the spring should look near the church remains, though the water may be difficult to identify depending on the season and weather conditions. The 1863 Ordnance Survey map, available to view through the OSi historical map portal, gives the clearest indication of its recorded position.