Just like most other regions, the Kanto region has many Gyms located throughout the towns and cities. In the Generation I games (Red and Blue), Generation II games (Gold and Silver), Generation III remakes (FireRed and LeafGreen), Generation IV remakes (HeartGold and SoulSilver), and Generation VII remakes (Let's Go, Pikachu! and Let's Go, Eevee!), there are a total of 8 Gyms. In the Pokémon Anime, the main character, Ash, battled at eight Gyms as well. However, as seen with several characters' Badges, there were other unidentified Gyms that were not shown in the games.
Pewter City Gym
The Pewter Gym (Japanese: ニビジム Nibi Gym) is the first Pokémon Gym that you battle in the Kanto region if playing a purely Kanto game. If you are playing a Johto game, however, this is the 6th Kanto Gym.
Based on its name, the gym strictly uses Rock-type and Ground-type Pokémon. It's located in Pewter City, which is located just north of Viridian Forest. Brock is the leader of this gym. There is only 1 gym trainer in Red and Blue, Gold and Silver, and FireRed and LeafGreen. In HeartGold and SoulSilver, and Let's Go, Pikachu! and Let's Go, Eevee! however, there's a total of 2 gym trainers in the gym, however, they can all be avoided by walking around them.
Cerulean City Gym
The Cerulean Gym (Japanese: ハナダジム Hanada Gym) is the second Pokémon gym in the Kanto region if playing a purely Kanto game, if playing Gold and Silver, it is the 4th Kanto Gym and if playing HeartGold and SoulSilver, it is the 5th Kanto Gym. It is located in Cerulean City which is and the leader is Misty. She is a user of Water-type Pokémon. The path is simple and contains Two trainers in Fire Red and Leaf Green. One trainer can be avoided by taking the alternate path and the other can be avoided if player talks to Misty from her left. Hence, energy can be saved to directly Battle the Gym leader.
Vermilion City Gym
The Vermilion Gym (Japanese: クチバジム Kuchiba Gym) is a Pokémon gym in the Kanto region. It is located in Vermilion City and the leader is Lt. Surge. He is a user of Electric-type Pokémon. There are several dustbins in the Gym and player has to guess the correct order or checking the bins. Once the player finds the first switch hidden inside one of the bins, the other switch has to be in the adjacent bin but in any direction. Two trainers can be avoided and one has to be battled. Then player can battle Lt. Surge.
Celadon City Gym
The Celadon Gym is located in Celadon City. The leader is Erika. She gives out the Rainbow Badge and uses Grass-type Pokémon as her speciality. The gym conatins three paths that can be used to reach Erika in Fire Red and Leaf green. For the central path, player can avoid the first trainer but the has to battle other and vice versa. Then player has to use Cut on the thin tree present and has to battle another trainer. Then, Erika can be battled if player moves straight. If moved left or right, another trainer comes for battle. If used the left or right path, the trainer can avoid all trainers and cut the tree. After cutting it, the player has to battle at least one trainer, and then battle Erika.
Fuchsia City Gym
The Fuchsia City gym is in Fuchsia City. The leader varies in the games. In Red/Blue/Yellow, Koga is the leader, but in HeartGold and SoulSilver, Janine, Koga's daughter, is the leader. Both focus on the Poison-type. Like the other gyms, this uses a special tactic against the player. The gym leader uses a series of invisible walls to confuse new trainers. In some games, the outlines of the walls can be seen and avoided.
Saffron City Gym
Saffron City's Gym Leader is Sabrina, who uses Psychic-type Pokémon. There are teleporting tiles that the player must use in order to get to the gym leader. The Gym contains 7 trainers. However, these trainers can be avoided by walking on the bottommost layer of tiles.
Cinnabar Island Gym
The Cinnabar Island Gym leader is Blaine. He gives out the Volcano Badge, and he uses Fire-type Pokémon. The gym contains 7 trainers in Fire Red and Leaf Green. However, these trainers can be avoided very easily. There are small machines in every cell where a trainer stands. Those machines ask Trivia questions which if answered correctly opens the door. Otherwise, the player faces a trainer. This can be done alternately by not answering the questions but by battling the trainers. In Gold, Silver and Crystal, the volcano on Cinnabar Island had erupted and everything was destroyed except for the Pokémon Center, so Blaine had to relocate to the Seafoam Islands. In HeartGold and SoulSilver his Gym was redesigned and had trainers.
Viridian City Gym
Viridian City's Gym Leader, in Blue, Red, Yellow, Fire Red and Leaf Green is, somehow, the Team Rocket leader Giovanni, who uses Ground-type Pokémon. The gym contains Motion Pads that send the steppers to the direction pointed by the arrowon it. Player has to choose the correct motion pad to avoid trainer and battle the leader. This can be done alternately by battling trainers yourself. In Heartgold, Soulsilver, Gold, Silver and Crystal versions; the leader is Blue who uses all types of Pokémon.