there is no key you first have to complete the mission of stopping the legendries then the gym leader will invite you or you can go there or whatever
shutup
The 8th Gym Leader in Pokémon Sapphire can be found in Sootopolis City.
Sootopolis City
Wallace he was the former 8th gym leader in ruby and sapphire
Go through the cave of origin.
You might need to open the door to the 8th gym in Pokémon Ruby, Sapphire and Emerald. To do this you first have to awaken Rayquaza.
There is no key for the 8th Gym. You have to look for Wallace in order to access the gym. He's located in the Cave of Origin, which is directly north of the gym.
You have to get Kyogre and then go to the ciuty it is in and got to the chamber.
He's the 8th gym leader. Juan is the 8th leader in emeraled and wallece is the elite four champion.
In Sootopolis City.Trainers and Gym Leader uses Water-Type Pokemon.
u have to defeat the 8th gym leader in that same town
You need the 8th gym badge. You obtain the HM itself in the Cave of Origin.