It measures barely half a metre in length and not quite a quarter of a metre deep, which makes it easy to overlook as anything other than a hollow in the stone. But this unassuming basin has accumulated at least four different names over the centuries and a tradition of healing that predates any written record of the place.

By 1777, Taylor and Skinner's road maps of Ireland had marked it as a spa, which at the time simply indicated a mineral or otherwise notable spring, not the kind of establishment the word suggests today. The 1911 Ordnance Survey six-inch map gave it the name Toberhullamag, though folklore collectors working in the area recorded it under several other forms: Tobar Hullamuck, St. Colman's Well, St. Colmach's Well, and St. Mocholmog's Well. The clustering of these names around a single saint suggests the same figure remembered differently across townlands and generations, the Irish name Colmog or Colmoig being a diminutive form associated with several early medieval holy men. The tradition attached to the well is specific and vivid: a saint struck the ground here to produce water for the baptism of a pagan chief, and the well's waters are said to cure sore eyes. A concrete plaque erected in 1913 formalises this connection, carrying a plain cross and the Irish inscription "A Colmoig Naomhtha guidh orainn, Tobar Colmoig, 1913", which translates roughly as "O holy Colmoig, pray for us, Well of Colmoig, 1913". The plaque gives the site a fixed point in time even as the names around it remained fluid.