Tobersenan, on Scattery Island in the Shannon Estuary, has none of these. The well sits quietly about twenty-two metres west of the island's distinctive round tower, built into the lowest of a series of natural terraced steps where the ground rises to the west. It is an unusually large structure for a holy well, a rectangular spring measuring roughly three and a half metres east to west and just over a metre and a half north to south, enclosed by a thick drystone surround. Two steps lead down from the eastern approach to water that drops immediately to a depth of over a metre, and the western wall rises a full metre and a half above the surface. The scale gives it a slightly austere, almost formal character.

The well takes its name from St Senan, the sixth-century monastic founder traditionally associated with Scattery Island, known in Irish as Inis Cathaigh. A pattern, which is a localised religious gathering combining prayer with communal ritual, was held here on 8th March, the feast day of St Senan. Whether that gathering continued into recent centuries is unclear, and no votive offerings remain to suggest active present-day use. A cross-marked slab recorded by the antiquarian Thomas Johnson Westropp in 1897 has since disappeared entirely, leaving one fewer fixed point in what was already an uncertain history. It is not even clear that the well as it now stands is an original construction rather than a later intervention built around a natural spring.