Aone Island was a long, narrow isle of hard black stone south of the Brimstone Breath, stretching roughly ten miles from its high eastern cliffs to its low western shore. The rock rose sharply from the sea in most places, broken only by narrow shelves and wind-cut ledges where snow and ice collected. Along the western shores exposed to open ocean air, ice sheets could form and break apart Aone Island's rocks, creating impassable areas for ships. Even when exposed, the island's surface was largely barren, with little soil and no sustained vegetation beyond lichen.
Technically under the banner of the Common League, Aone Island was the last Common stop by sea before one could reach the Sound of Silveril. An old path crossed the island from east to west, worn directly into the stone by centuries of use, though it saw little traffic after the Aonefort was established. The path connected the eastern approach to the prison complex on Breakbleak Rock, and beyond that purpose it led nowhere of consequence. No permanent communities took root on Aone Island, as the cold, isolation, and lack of arability discouraged settlement.
Temperatures remained below freezing for most of the year, dropping to as low as thirty degrees below zero around the time of Bleaksummit, and only the presence of the prison and its garrison gave the island any lasting Human presence at all.