In Pokemon FireRed and LeafGreen you can't open a gym.
You will find the key to the Gym of Cinnabar Island, From the Pokemon Mansion that is on the same island.
I think the gym in fuschia city
After defeating Blaine at Cinnibar Gym, you must return to Viridian City. The gym will now be open, and after defeating the leader, you'll get the Earthbadge.
The sixth gym leader,Sabrina, is in Saffron City.
The 6th gym is in Saffron City the gym leader is Sabrina she uses Psychic type pokemon.
at channabr island
In Fuchisa city
in fuchsia city
You have to go into the pokemon mansion, find your way through it, and pull a switch and the gym will open.
To open the Elite Four, you have to get all the Gym badges.
In Pokemon FireRed and LeafGreen you can't open a gym.
You must beat team rocket at silph co before you can enter the 6th gym.
to open the door of the 7th gym!
Open the door and challenge the gym leader.
It's in Cinnabar island. It's where you get the key to open the Gym #7
You will find the key to the Gym of Cinnabar Island, From the Pokemon Mansion that is on the same island.