go to cinnabar island then go into Pokemon mansion go through here to get the secret key which opens the 7th gym.
After obtaining the other 7 badges you return to Viridian City and the gym will be open.
Get the key from the basement of the mansion next to the gym.
You have to go to the Pokemon mansion, This mansion is located in thee same town as the 7th gym leader. In the Pokemon mansion there will be many ways to walkthrough. (Hint, The mewtwo statues have switches.)
You must beat the seven gym leaders, the elite four, and your rival. Then you have to capture 60 Pokemon to get your Rainbow pass the will allow you to travel to Island 7 in Pokemon FireRed.
It is atchrily the 8th gym. It will open when you get the first 7 gym badges
It's in Cinnabar island. It's where you get the key to open the Gym #7
Just like in FireRed/ LeafGreen versions, you must have 7 badges.
You need the secret key which is found in Pokemon mansion which is also on cinnibar island.
Get a Pokemon who knows cut and use it on the door. You can't just press "A" at the door though you have to open your Pokemon menu and do it from there.
Their are 7 HM's available in Firered.
The seventh gym is on Cinnabar island,right down of pallet town.To open the doors you must reach to a certain room of the Pokemon mansion.You get a key and open the seventh gyms doors,and the gym is a fire gym
in 4-7 islands