From Bulbapedia, the community-driven Pokémon encyclopedia.
GR Island in Pokémon Card GB 2
GR Island is an island found in Pokémon Card GB2: Here Comes Team GR!. It is the home of Team Great Rocket. It contains eight forts/altars/strongholds, the Challenge Hall, a Game Center, Mr. Ishihara's Villa, the GR Castle, and an Airport.