Pokémon Red and Green are primarily set in the fictional region of Kanto.
Kanto is the world explored by the player in the first-generation Pokémon games. The player travels through towns, routes, caves, forests, and seas while collecting Pokémon, challenging eight Gym Leaders, and attempting to become the Pokémon League Champion.
The region’s name was inspired by the real Kantō region of Japan, although the game world is a fictionalized setting. Important locations include Pallet Town, Viridian City, Pewter City, Celadon City, Fuchsia City, and Cinnabar Island. The game’s design established the region-based structure that later Pokémon titles continued.
Kanto is sometimes confused with the game versions because international players first encountered it through Pokémon Red and Blue, while Japanese players began with Red and Green. The region itself is the same broad setting. Kanto also reappears in Pokémon Gold and Silver, where it can be explored after the player completes the Johto portion of the story.