Saint Finan's Cell on Church Island is a drystone structure whose walls average over two metres in thickness at the base, a figure that places it well beyond anything you might loosely call a simple hermit's shelter. The stones used in its construction were almost certainly hauled from the lakeshore nearby, and the overall effect is of something built to endure rather than merely to serve.

The cell is rectangular in plan and sits close to the western shore of the island, connected by a causeway to its eastern end. Its external walls bow slightly outward and curve at the corners rather than meeting at sharp right angles, a feature that distributes weight and gives the structure an oddly organic profile. The technique used throughout is corbelling, where successive courses of stone are laid so that each one projects inward slightly over the one below, gradually closing the space above without the need for an arch or a vault. The doorway in the north-east end-wall is trabeate, meaning it is spanned by a flat lintel rather than an arch, and three massive slabs roof the opening. Above the main doorway on both sides, and again in the south-west end-wall near ground level, there are small lintelled openings, narrow enough that light and air were their most likely purpose. The walls reach a preserved height of just over three metres, and the construction shifts partway up from the largest foundation stones to thinner slabs, coinciding with an external offset or ledge that runs around the building at roughly head height. Saint Finan himself is associated with a number of early Christian sites across Kerry and the wider south-west of Ireland, and the island setting is consistent with the early medieval monastic preference for places set apart by water, whether sea, river, or lake.

The interior has been partly divided by a wall that appears to be of more recent date, and a short run of similar walling is visible on the exterior at the north-west. These later interventions do not much distract from the overall impression of the original fabric, which remains remarkably coherent for a structure of its age and construction type.