A crannog is an artificial or partly artificial island, typically built during the early medieval period as a defensible dwelling place, constructed from timber, stone, peat, and brushwood piled up in shallow water. The one recorded at Aroddy appears on that single map edition as a small island of roughly ten metres in diameter, sitting about ten metres from the southern shore of the lough, which is a triangular body of water stretching approximately 1.2 kilometres east to west and 900 metres north to south.

What makes this site quietly puzzling is the gap between its cartographic presence and its physical absence. It appears on the 1911 map and nowhere else, and today there is no visible evidence of the structure at all. One plausible explanation is that the island has gradually been absorbed into the lakeshore over time, its material merging with the bank so completely that the boundary between the two has been lost. Whether the original island was a genuine early medieval crannog or something more modest, perhaps a natural feature that was partially improved or simply mistaken for something more deliberate, is impossible to say from what remains.