you have to get to the top of mt.coronet and fight team galactic and catch or kill dialga.
then go to sunnyshore city the guy will let you thru.
then walk thru the path and boom.
sunnyshore and the 8th gym!
In Diamond, Pearl and Platinum 7th gym is in Snowpoint Town.
the seventh gym badge snowpoint gym
you beat the gym leader
Hearthome
Sunnyshore City Gym: Electric (beacon badge from Volkner)
In Diamond, Badge 5 can be gotten by defeating Fantina in her Gym in Hearthome City.
you beat everyone in the gym
beat the league
snowpoint city
beat the #?*@! gym leader
By beating the gym leader
The Relic Badge is given to you by Gym Leader Fantina of Hearthome City (Gym #5).