The altar is modest in scale, roughly 1.6 metres long, 1.12 metres wide, and standing 0.9 metres high, yet it carries a detail that rewards close attention: one of the two capping flagstones bears the letters "IHS" deeply incised into the stone, and rising from the horizontal bar of the H is a small Latin cross with triangular terminals. The initialism IHS is a Christogram derived from the first three letters of the Greek name for Jesus, and its appearance here, carved with evident care into rough limestone, gives an otherwise unassuming structure a concentrated sense of purpose.

The altar is built from undressed limestone blocks, the kind of unworked, irregular stone that characterises vernacular religious construction in the west of Ireland, and it was set deliberately against a natural limestone rock face immediately to its west, using the living geology of the island as both backdrop and partial support. This relationship between the constructed and the natural is not incidental; holy wells and their associated altars across Ireland were frequently sited where the landscape itself seemed to participate in the sacred arrangement. The well here is dedicated to St Eany, the saint also commemorated in the place name Cill Éinne, which translates roughly as the church or cell of Éinne. Éinne, also known as Enda, is associated with one of the earliest and most significant monastic foundations in early Christian Ireland, and the presence of both well and altar in this location speaks to a continuity of religious attention stretching back many centuries.