Uncovered during a 1994 dig, this small rectangular structure measures just under eight metres east to west and five and a half metres north to south, its walls built from carefully laid flat schist flags without mortar. What makes it quietly arresting is not its size but its engineering: the bedding joints of the stonework tilt slightly outward to shed rain, the southern wall and corner are cut into the bedrock itself to a depth of 0.7 metres, giving the interior the feel of a sunken room, and evidence on the south and east walls points to a corbelled roof, meaning the stones would have been cantilevered inward in successive courses until they met at the top, requiring no timber at all. The doorway, just 0.68 metres wide, sits in the east wall rather than the west, which is unusual for early medieval Irish church architecture. The likely reason is practical: the prevailing south-westerly winds at that exposed altitude made a westward entrance untenable.

Radiocarbon dating of charcoal found inside places the building's use somewhere between 430 and 890 AD, firmly within the Early Medieval period. In form, it resembles the famous Gallarus Oratory on the Dingle Peninsula, a boat-shaped corbelled stone structure that has survived largely intact, and it may have functioned in a similar way, as a small oratory for prayer or liturgical use at a site already carrying enormous religious significance. The excavation recovered three sherds of native medieval pottery dating to the thirteenth through fifteenth centuries, two corroded bronze pins, worked flints, and fragments of iron, suggesting the building continued to see some use or activity long after its original construction. A spread of charcoal near floor level, divided by a line of flagstones, remains unexplained. When the structure was first identified, it was assumed to be Temple Patrick, a church marked on the 1838 and 1920 Ordnance Survey six-inch maps and recorded in local tradition. But the dimensions and the position of the doorway do not match the description given in the 1838 OS Letters for that building, so the two are now understood to be distinct. Documentary sources hint at the deep continuity of religious structures on the mountain: church taxes are referenced in records from 824 AD, and a church at Cruachpatric appears in a papal epistle of Pope Honorius III from 1216, suggesting that building and rebuilding on the summit stretched across many centuries.