The Ice Key, as its name implies, is a large key made of ice. It is one of the players in the Stop 'n' Swop mystery, first being found in Banjo-Kazooie, and again in Banjo-Tooie where it can be utilized.
In Banjo-Kazooie, the Ice Key is found in Wozza's cave in a large alcove, although the room is blocked by an unbreakable transparent wall. Entering the code "CHEAT NOW YOU CAN SEE A NICE ICE KEY WHICH YOU CAN HAVE FOR FREE" on the Sandcastle floor in Treasure Trove Cove will dissolve the wall, allowing the player to get the key; however, as with the other Stop 'n' Swop items, it has no apparent function in Banjo-Kazooie.
In Banjo-Tooie, it is possible to obtain the Ice Key without the use of cheats. In Jinjo Village, just to the right of the entrance, there is a small icy cavern which can be accessed using the Grip Grab. There is a Banjo-Kazooie Game Pak inside which will yield the precious Ice Key when defeated. Take the Ice Key to the Waterfall Cavern in Glitter Gulch Mine and use the Talon Torpedo learned from Jolly Roger's Lagoon on the Kazooie boulder in the water. Swim through the tunnel that opens up to a large room on the Icy Side of Hailfire Peaks containing a gigantic ice safe. The key can be used to unlock the safe, revealing the powerful Mega Glowbo which can be brought to Humba Wumba in the Pine Grove to transform Kazooie into the fearsome Dragon Kazooie.
In Banjo-Kazooie: Nuts and Bolts, the ice key will activate a crate on the roof of Boggy's Gym. This crate gives you the British flag. lol lol i edited it :P