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 key is a small puzzle involving HM04 (Strength) that, when completed, allows Unown to be captured in the Tanoby Chambers. The puzzle consists of several boulders that must be maneuvered into a correct pattern that will unlock the Unown, allowing them to be caught.
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