The Viridian Gym is a location within the Pokémon video games and the Indigo League anime series. It is in the town of Viridian City and led by Gym Leader Giovanni, who specializes in Ground-type Pokémon.
In Pokémon SoulSilver and HeartGold, the Viridian Gym is not accessible. This is because the games feature the Johto region, rather than the Kanto region where Viridian City is located. Instead, the player must challenge the Johto Gym Leaders, which include Bugsy, Falkner, Whitney, Morty, Chuck, Jasmine, Pryce, and Clair, in order to earn the Johto League Badges.