The well takes its distinctive octagonal shape, a design choice that sets it apart from the more common circular holy wells found throughout Ireland. This geometric precision suggests deliberate construction, possibly dating to a period when such springs held deep religious significance for local communities.

The well sits on the south-southwest slope of a substantial cairn, a stone mound measuring roughly 6.3 metres by 4.9 metres and standing nearly a metre high. Such cairns often mark prehistoric burial sites or serve as territorial markers, though this particular example remains unclassified by archaeologists. The positioning of the well in relation to the cairn hints at a possible ritual connection between the two features, a pairing commonly seen at Irish sacred sites where water sources and ancient monuments create layers of meaning across different historical periods.

St. Carthach, also known as St. Carthage, was a 7th-century bishop who founded the monastery at Lismore in County Waterford, though his influence spread throughout Ireland. The dedication of this Donegal well to him suggests either a local connection to the saint or the later Christianisation of an existing pagan spring. Today, the site remains accessible in its pastoral setting, offering visitors a glimpse into the complex religious landscape of rural Ireland where prehistoric monuments, early Christian dedications, and natural springs converge in the same sacred space.