Known as Cell E, this is the largest of the clochán on the site; a clochán being a corbelled stone hut, built without mortar, in which courses of flat stones are laid so that each projects slightly inward over the one below until they meet at an apex. What distinguishes Cell E is not just its size but the elaborateness of its construction, suggesting it held particular importance within the monastic community that occupied the island.

The building sits on a broad stepped platform that rises more than three metres above the main terrace to the south-east, reached by two successive flights of steps, the lower ascending to a platform level, the upper continuing to the doorway itself. That doorway is 1.34 metres high and narrows as it rises, tapering from 0.85 metres at the base to 0.65 metres just under the lintel, a form typical of early medieval Irish ecclesiastical architecture. The domed interior measures 3.8 metres square at floor level, with the floor itself flagged in large slabs and sloping gently down towards the entrance. Inside, five stones project from the wall at roughly 1.7 metres height, possibly serving as pegs or supports, while four recesses set at 2.25 metres, arranged in two opposed pairs, may have functioned as beam-holes to carry a timber fitting of some kind. The external face of the dome bristles with projecting slabs, and two horizontal offsets or ledges run around the outside above doorway level, the uppermost circling the entire building. The dome itself reaches 3.6 metres in height and retains an aperture at the top. The description above draws on survey work published by O'Sullivan and Sheehan in 1996, and the building is also visible in a LiDAR survey of the monastery published by Bourke, Hayden and Lynch in 2011, where it is labelled as structure number fifteen.

Cell E sits on the north-east side of Cell D, and close to two leachta, which are flat-topped stone commemorative or funerary monuments associated with early Irish monasticism. Together these features suggest the north-east part of the terrace carried particular ritual or residential significance within the wider complex.