Location from pokemon-kanto by
The final gym of the Kanto circuit — hidden in plain sight as a publicly licensed gym while secretly doubling as a front for Team Rocket's boss Giovanni.
Viridian Gym feels wrong the moment a trainer steps inside. It is too quiet. The staff are silent. The air smells of ozone rather than the usual Pokémon-gym musk. When Ash finally arrives at the end of his Kanto circuit, he finds Team Rocket's Jessie, James, and Meowth running the gym for Giovanni in his absence (he's rebuilding after Mewtwo's escape). Their mechas replace the usual battle — and Pikachu destroys them. The Earth Badge is left behind with the trio, who hand it over in humiliation and watch Ash leave.
An imposing black-and-red building at the north edge of Viridian City, windows tinted, a giant stylized 'R' discreetly worked into the floor tiles inside. The battle arena floor is a rough earth-and-rock field suitable for Ground-type Pokémon. A raised dais at the back is Giovanni's seat, usually with his Persian at his feet.