A shallow hollow cut into the bedrock, roughly twelve metres long and no more than a quarter of a metre deep, preserves what appears to be the earliest evidence of human activity at the site. It is not a grand structure by any measure, but what was found inside it complicates any simple story about when this famous place began.

The hollow, one of three similar features exposed during excavation of the inner enclosure of Dún Aonghasa, had a rough, irregular northern end and a more carefully trimmed southern portion, which was packed with occupation material. Radiocarbon dates taken from animal bone in that southern half returned results of approximately 1500 to 1390 cal. BC and 1460 to 1120 cal. BC, placing activity here firmly in the Middle Bronze Age, well before the fort's construction. The finds recovered from the hollow range considerably in character: pottery, an amber bead, a bronze chisel, copper slag, clay mould fragments, pumice, bone points, needles, pins, bone handles, scraps of iron, and a bronze tweezers. The copper slag and clay mould fragments suggest metalworking of some kind, while the large quantities of animal bone and shell indicate that part of the hollow was used as a midden, a domestic rubbish deposit, though whether from the very beginning could not be established with certainty due to later disturbances, including a burial cut into the same area. Excavators could not determine whether the hollow served as a living space, a working area connected to seasonal activities such as cliff fishing, or something with a more ritual character. The artefact assemblage points to continued use into the Late Bronze Age and possibly beyond, meaning this unremarkable scoop in the rock was, in some form, in use across several centuries.