How do you get to the Pokemon league in Pokemon Platinum?

Answer 1

go to sunyshore city use surf on the route make sure you beat volkner any way use surf on the route keep going strate and use waterfall on the waterfall you will see a cave entrance go threw cave and use waterfall theres the POKEMON LEAGE

Answer 2

After beating Sunnyshore gym use surf on the water north of the Pokemart. You will see a big waterfall. If you didn't teach or find the HM Waterfall, teach it to one of your Pokemon now. Heal your Pokemon, then go through Victory Road. It's a long way! You will see a big castle, and that's the Elite Four league!