A hollow in the rock, now buried beneath the terrace of the fort's inner enclosure, preserves that earlier occupation in fragmentary but telling detail. What looks from above like a simple depression in the bedrock was once, before the walls went up, a natural platform, its sheer rear face most likely formed by stone being prised away along a geological fault line.

Excavations at Dún Aonghasa, the great prehistoric cliff fort on Inis Mór in the Aran Islands, investigated this hollow, recorded as feature F1009, within what archaeologists designated Cutting 11 in the east sector of the inner enclosure. The earliest deposits on the rough, uneven floor of the platform contained dispersed organic residues and nine sherds of coarse cooking pottery, enough to indicate domestic activity even though no structural remains survived. Animal bone from this earliest layer returned a radiocarbon date placing activity somewhere between roughly 1170 and 890 cal. BC, deep in the Irish Bronze Age. Above that, an irregular setting of stones appeared to define a small semicircular area, and associated finds told a more specific story: large quantities of burnt sandstone and a fragment of burnt quartzite, along with a considerable number of limpet shells, animal bones, and some fish bones. The assemblage points strongly to a hot-stone roasting pit, a cooking technique in which stones are heated in fire and then used to boil or roast food. Animal bone from this second layer was dated to between approximately 980 and 810 cal. BC. Taken together, the two horizons suggest repeated use of the same sheltered spot across what may have been several generations, all of it predating the enclosing wall that eventually swallowed the eastern edge of the platform entirely.