Rimegate is one of the abandoned castles of the Night's Watch, standing on the Wall between Sable Hall and Long Barrow. Its name comes of the rime that sheathes its gate and battlements through the long northern winters.
Sealed in Ice
Each castle of the Wall was built to guard a passage through the ice, and when Rimegate's garrison was withdrawn its tunnel was packed with stone and ice against any who might try it from the north. So the castle keeps a kind of watch even empty, its frozen gate as stubborn as any warden, while the brothers of Eastwatch and Castle Black ride the top of the Wall above its silent towers.