Players must defeat eight Gym Leaders in the original Pokémon Red and Blue games.
Each Gym Leader specializes in a particular Pokémon type or battle style and awards a Badge when defeated. The Badges serve as proof of progress and allow the player to use certain field techniques or control higher-level traded Pokémon.
The Kanto Gym Leaders include Brock, Misty, Lt. Surge, Erika, Koga, Sabrina, Blaine, and Giovanni. Their Gyms are spread across the region, although the player’s route through them is not always completely linear.
After collecting all eight Badges, the player can challenge the Pokémon League at Indigo Plateau. That final challenge consists of the Elite Four and the current Pokémon League Champion, making the Gym circuit the main structure of the original adventure.