Castle Black is the principal seat of the Night's Watch, where the Lord Commander keeps his tower at the heart of the Wall's defenses. The kingsroad runs to its gate from the south, from Mole's Town and the lands of the Gift, and here new brothers say their vows and take the black.
A Castle Without Walls
Like all castles of the Watch, Castle Black has no walls of its own, only its keeps and towers standing open to the south, for the black brothers swore to take no part in the wars of the realm and built no fortress that could be held against it. Its only rampart is the Wall itself, looming seven hundred feet above the yards.
Stair and Cage
Men reach the top of the ice by a great switchback stair of wood anchored to the Wall, or by the winch cage that hauls them up by chain, while in deep winter the brothers pass between keeps through tunnels beneath the snow that they call the wormwalks.