It is known locally as Tobar an Tóin Dubh, a name that translates roughly as the Well of the Black Bottom, and its shape is distinctive: a round depression in the rock with one section of the rim drawing out into a broad, pointed projection. It is not a constructed well in any conventional sense, but a feature of the coastal geology that has accumulated layers of ritual significance over time.

Holy wells, of which Ireland has thousands, are sites where springs, rock pools, or other water sources became focal points for veneration, often blending pre-Christian practice with Catholic observance. The customs attached to Tobar an Tóin Dubh are specific and particular. According to local tradition, the well should be visited on Mondays and Fridays, and on each occasion the visitor makes nine rounds of the site, a pattern of circumambulation known elsewhere in Ireland as a turas or station. The number nine recurs frequently in Irish well traditions, and the prescription of particular days of the week, rather than a single feast day, gives this site a slightly different rhythm from wells tied to a named saint's calendar. The detail was recorded by Tim Robinson, the writer and cartographer who spent decades mapping and documenting the Aran Islands and Connemara with extraordinary thoroughness, and whose work preserved many localised traditions that might otherwise have gone unrecorded.