Constructed from limestone and concrete blocks and capped with a rough square flagstone, it measures less than a metre in length and stands only about forty centimetres high. It is the kind of thing you might walk past without registering, until you notice the inscribed plaque mounted above it, dedicated to a saint most visitors will never have heard of.

The enclosure itself appears on the Ordnance Survey six-inch maps under the name 'Aharla', and it sits within the townland of Cill Éinne, whose name, meaning 'church of Enda', points to the early medieval monastic tradition for which the island is known. The altar is dedicated not to Enda, however, but to St Ronane, a figure whose connection to this particular spot is not fully documented but whose name surviving here in stone and mortar suggests a long, localised memory of veneration. The structure is clearly a modern construction, built in the manner of a traditional wayside altar, where a flat stone surface is set against a wall to allow for the placing of offerings or the saying of prayers. That tradition, common across rural Ireland, often preserves the memory of older sacred sites even when the original physical fabric has long since disappeared or been absorbed into later field boundaries and enclosures.