it is in veriden city.
beat Giovanni in saffron, beat the 7th gym finish the quest on the islands and go to viridian city. the gym over there is the 8th gym.
In his gym
the 5th gym is saffron gym with sabrina!
Misty
wermilion city gym badge (electric type gym)
Sabrina's gym in saffron city
I think the gym in fuschia city
It depends on what gym you are talking about all of them you can get to by going to the towns.
in the mansion.
In Cerulean city.
In the Kanto region, the sixth gym is in Saffron City. The gym leader is Sabrina.
The fifth Gym Leader in Pokemon LeafGreen is Koga, the leader of Fuschia City's Gym. He specializes in Poison-type Pokemon and hands out the Soul Badge.