The difficulty is that nobody can agree precisely where it is. Three separate water sources have each been put forward as the genuine article, and the matter remains unresolved, lending the well an unusual quality for a sacred site: it is, in a sense, simultaneously in multiple places and nowhere at all.

The three candidates were recorded by the folklorist Caoimhín Ó Danachair in 1958. The first is the Spa Well, located at the north-western end of the Zoological Gardens. The second is the Poor Man's Well, which sits beside Blackhorse Avenue along the park's northern boundary. The third is a well found in the moat of the sunk fence, a ha-ha style ditch used to create an unobstructed boundary without a visible wall, positioned beside the western gate of Áras an Uachtaráin, the Irish presidential residence. All three lie within a relatively compact area, and all three have at some point carried the association with St Fintan, though Ó Danachair's account makes clear that no single identification had been firmly established. Holy wells in Ireland were typically associated with a local saint and visited for purposes of healing or devotion, with patterns, or annual communal gatherings, held on the saint's feast day. That this particular well's location had already become uncertain by the mid-twentieth century hints at how quietly such traditions can fade.

Visitors with an interest in tracking down the candidates will find all three sites accessible within Phoenix Park, one of the largest enclosed public parks in any European capital. The Spa Well and the Áras an Uachtaráin gate well are closest together and could reasonably be visited in a single walk. The Poor Man's Well near Blackhorse Avenue requires a short detour towards the northern perimeter. Given the uncertainty, it is worth treating all three locations as points of interest in their own right rather than searching for a definitive answer that the historical record does not yet supply.