You will need to use the Secret Key which is hidden in the basement of Pokemon Mansion which is located on Cinnibar Island.
The key is in the Pokemon mansion.
in the mansion.
On cinnibar island.
its actually the 8th gym so you need 7 badges and then it will unlock
It unlock the door to the gym in Viridian City. .
Cinnabar Island. To enter you have to find a key in the mansion nearby.
seventh badge is cinnabar island. Fly to Pallet Town, surf south. Then go into pokemon mansion and find the secret key to unlock the gym
You have to find the key in the abandoned mansion.
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
Beat the seventh gymleader and when you come out of the gym a guy will give it to you
The gym in Viridian is actually the last gym. You'll unlock it after getting all the other badges. You should continue to Pewter through Viridian Forest.
The basement.