A narrow causeway threads along the northern shore connecting two distinct zones of activity: at the eastern end, a Romanesque church, a burial ground, ten cross-inscribed slabs, three leacht structures (low stone cairns associated with penitential prayer), and uninscribed pillar stones; at the western end, St Finan's Cell, a corbelled dry-stone structure of the kind associated with early Irish monasticism. Between them, old field boundaries and the foundations of several rectangular house sites fill much of the remaining ground, suggesting this was once a functioning community rather than merely a place of worship.

The island is associated with St Finan Cam, said to have founded a monastery here in the sixth century, and it appears in the Annals of Inisfallen under the name 'Inis Uasail' in 1058. By 1302 to 1306 it was listed in the Papal Taxation records for the diocese of Ardfert, and its rectory is mentioned again in 1418. By 1622 it was recorded as the sole surviving prebend of the ruined church of Aghadoe, a measure of how far the institution had contracted. The Romanesque church of St Finan, dating in its nave to the late twelfth century with a chancel added shortly after 1200, was recorded by both Windele and Dunraven before the Office of Public Works conserved and partially rebuilt it in the 1880s. That intervention was imperfect: some voussoirs in the elaborately carved west doorway were repositioned incorrectly, and portions of columns are missing. The doorway itself repays close attention. Wrought in reddish-brown sandstone with jambs of four orders, it carries scalloped capitals, spiral roll-mouldings, chevron ornament, and a capital on one jamb bearing a pair of carved ornithomorphs, possibly swans, facing one another. A single carved anthropomorphic head survives in situ as a hood-mould stop on the south side.

Inside the chancel, cemented to the surviving south jamb of the chancel arch, is a carved sandstone block known locally as the Fiddle Stone: a figure playing a bowed stringed instrument, rendered in relief within what appear to be remnants of a moulded decorative border, suggesting the stone may once have formed part of a larger frieze. Nearby, the stone altar against the east gable contains a small niche near its base, possibly a relic cavity, in which human bones have been found. A locally venerated object, described as St Finan's altar stone, was cemented to the altar's surface until it disappeared at some point in recent decades. The island's Irish name, Oileán an Teampail, simply means Island of the Church, which in its plainness rather undersells what survives there.