Ice Dragon (constellation)
The Ice Dragon's blue eye points north. Following the Ice Dragon's tail will take you south. The Ice Dragon also appears in the tales of Old Nan. She told that the breath of the Ice Dragon was very cold.
On the way to Standfast with his squire, Aegon Targaryen, Ser Duncan looks up to the night sky and sees, among other constellations, the Ice Dragon. There are clouds in the north so the dragon's blue eye is obscured.
A Clash of Kings
A Storm of Swords
During their journey to the Wall, when Bran and his companions lost their way a few times, they needed only to wait for a clear cold night when the clouds did not intrude, and look up at the sky for the Ice Dragon. Bran remembers that the blue star in the dragon’s eye points the way north, as Osha had told him once.
The way's easy. Look for the Ice Dragon, and chase the blue star in the rider’s eye.