After the 7th badge, you sill need the 8th.It should be the badge from whatever city [that has a gym] that you haven't been yet.[After the 8th gym,you must go to the Pokemon League and beat the Elite Four].
after you get a gym bagdes . then you will go to a house vey close to the gym
The Seventh Kanto Gym Is At Seafoam Islands you get there from pallet town so go around that way hope it helped ;)
go to cicibar island, then go in the biulding right next to the gym and look for secret key. then get out and then you can go in the gym in cinabar island
Go back to your dad's gym and battle him, then go to the house next to it and get HM surf
After you beat your rival after the 6th gym
Mossdeep cityit is in mossdeep
to the 8th gym :p but seriosly i think u go to stooplis meaning u have to go under water about west form mosdeep
journey again to achieve the another battle called the 8th gym Pokemon ruby
after you beat the seventh gym, if you follow the gameplay, you'll get it
umm i dont know
in cave in dat one place
use dive in the dark water then go into a cave. ue dive again and you should be in sootapolis city
go right from the seventh gym leader
Use strong water or dark type Pokemon
In Pokemon Sapphire, Ruby and Emerald the 7th Gym that's located in Mossdeep City has Psychic type Pokemon.
go and beat the 8th gym
sootopolis city, after u awake rayquaza. the gym leader is juan, changed from ruby/Sapphire Wallace