This particular structure, known as Cell C, is a clochán, a type of dry-stone beehive hut built without mortar, its walls corbelled inward course by course until a single closing slab seals the dome at the top. The interior measures just 2.85 metres by 2.45 metres at floor level, a space barely large enough to lie down in, yet the dome rises to 3.55 metres, giving the tiny room a surprising vertical quality, almost like a stone tent pulled tight at the base and allowed to breathe upward.

The precision of its construction is quietly remarkable. The flagged floor slopes deliberately down toward the doorway, and beneath it runs a covered drain, a small but telling detail about how seriously the monks who built and used it approached the practicalities of living on an exposed Atlantic rock. The doorway itself narrows as it rises, measuring 0.64 metres wide at the base and tapering to 0.5 metres just under the lintel, with a height of only 1.34 metres, meaning anyone entering must duck. The southern external corner of Cell C was built so that its masonry sits on top of the adjoining Cell B, suggesting the structures were not all raised at the same moment but accumulated over time, each addition keying into what already stood. This layering gives the monastery on Sceilg Mhichíl something of a geological quality, its buildings accreting like the island itself.