From Bulbapedia, the community-driven Pokémon encyclopedia.
The Tanoby Key (Japanese: アスカナのかぎ Asukana Key) is a puzzle in Sevault Canyon on Seven Island in the Sevii Islands. Unlocking it is the key to releasing the Unown.
In the games
In Pokémon FireRed and LeafGreen, the Tanoby Key is a small cave on the mid-left side of the canyon. The puzzle inside consists of several boulders that must be moved using HM04 (Strength) into the room's craters, forming the correct pattern. When completed, this unlocks the Unown in the Tanoby Chambers and allows them to be captured.
In the manga
In the Pokémon Adventures manga
In the FireRed & LeafGreen chapter, Sird managed to unlock the secret of the Tanoby Key and gain control of the Unown, using them to defeat Lorelei in a Pokémon battle and to guard Trainer Tower later on, when she and her companions found out that Mewtwo had returned and was teaming up with Red to defeat them.
In other languages