The well at Carrownaglogh, north of Terryglass village, is small enough to overlook entirely, yet it carries a long devotional life concentrated into a very modest structure. Roughly circular in shape and no more than a quarter of a metre deep, it is enclosed by a low semicircular stone wall, and set into the inner face of that wall is a niche holding a small crucifix. The combination of the enclosed form and the placed object gives the site a contemplative intimacy that larger, more visited holy wells sometimes lack.

The well is dedicated to St Colmcille, the sixth-century monastic founder associated most strongly with Iona and Derry, though his cult spread widely across Ireland and left its mark on wells, parishes, and place names well beyond his immediate sphere of activity. The Ordnance Survey Name Books, compiled in the nineteenth century as part of a systematic effort to record local topography and oral tradition, note both the dedication and the specific belief that the water offers relief from headaches, a detail that roots the site in living folk practice rather than purely antiquarian record. The well sits close to a linear earthwork and a stream, and is understood to form part of the wider monastic complex associated with the area around Terryglass, a settlement with early medieval ecclesiastical significance on the western shore of Lough Derg.