Icemark is one of the abandoned castles of the Night's Watch, standing on the Wall between Hoarfrost Hill and the Nightfort. Its towers have stood empty since the Watch's dwindling strength forced the closing of castle after castle along the ice.
A Gate Unwatched
Every castle of the Wall guards a gate through the ice, and every empty castle is a gate that must be trusted to bars and cold rather than to men. Icemark's gate has long been sealed, its stores carried off and its brothers dispersed to the manned castles, though its stone keeps yet stand sound enough that a new garrison might one day wake them.