Altering Cave - Pokemon Fire Red and Leaf Green Guide - IGN

Found north of Sixth Island, this cave only have Zubats. However, if you have an E-reader connected to a gameboy advance using Japanese E-reader cards

Three Island - Pokemon Fire Red and Leaf Green Guide - IGN

Pokémon FireRed and LeafGreen Versions - Bulbapedia, the community

Altering Cave - Pokémon FireRed #49

Pokemon FireRed/LeafGreen Walkthrough - PokeDream

PK3/WC3: Unreleased Altering Cave Pokémon - Unreleased/Beta PKM

Pokémon FireRed & LeafGreen - Altering Cave

Three Island - Pokemon Fire Red and Leaf Green Guide - IGN

Celadon City - Pokemon Fire Red and Leaf Green Guide - IGN

Diglett's Cave - Pokemon Fire Red and Leaf Green Guide - IGN

Walkthrough - Pokemon Fire Red and Leaf Green Guide - IGN