An aumbry is a small wall-cupboard used to store sacred vessels or reserved sacrament, and its presence here suggests that this was a functioning, if modest, place of worship rather than a mere shelter or retreat. The whole structure measures roughly 6.9 metres in length by just under 4 metres in width, which makes it a very particular kind of early Christian building: an oratory, a single-cell chapel of the sort associated with the earliest wave of Irish monasticism, when individual holy men established themselves in remote or marginal places.

The oratory on Crump Island is associated with a saint named Rioch or Roc, a figure recorded by Whitley Stokes in 1868 and referenced by later antiquarians including Hardiman in 1846 and the compilers of the well-known county guide by Killanin and Duignan. The double name is not unusual in early Irish hagiography, where variant spellings and oral transmission across centuries could blur a single figure into something less certain. The oratory is oriented east to west, as early Christian practice required, placing the altar end toward Jerusalem. Immediately to the east of the building lies a small graveyard, and roughly thirty metres to the south-south-east there is a well, described cautiously as possibly holy, which is the kind of qualification that tends to reflect an absence of surviving folklore rather than an absence of significance. The cluster of oratory, graveyard, and well follows a pattern seen at early Christian island sites across the west of Ireland, where the sea acted less as a barrier than as a corridor for monastic settlement.