The Horn of Winter, also called Joramun's Horn, is the great warhorn that Joramun, an ancient King-Beyond-the-Wall, is said to have once sounded to wake giants from the earth. The free folk believe that whoever blows it will bring down the Wall, and Mance Rayder spent years searching the graves of the Frostfangs and the Milkwater for it, gathering the wildlings into a single host as much to find the horn as to flee the cold.
A great cracked horn ringed in old gold and graven with runes was found by Samwell Tarly and the direwolf Ghost in a cache at the Fist of the First Men, and later burned by Melisandre at the Wall as a show of power — though whether it was ever truly Joramun's Horn, none can say. If the true horn survives, it has not been found.
Status: lost.