you need to beat or catch giritina.
first u hav to get garitina then he lets u by
=you have to of done all seven badges to get there. You shold be able to after then. By the way the 8th gym is in sunyshore city.=
You have to have defeated the seventh gym leader in Snowpoint city
If you're talking about the guy blocking the path to Sunyshore city in diamond and pearl, you have to defeat Team Galactica at the top of the mountain, beat palkia, etc. After that the guy is gone.
perhaps you should go outside and make some friends
you have to have done the event at spear pillar.and then the guy who was the blocking the way to sunyshore city will be gone.
you need to capture/kill palkia/dialga at mt cornet and go to team galactic base in veilstone city
You have to go to Spear Pillar and do stuff there, everything will be explained on what to do once you are there
if you've cought giratina you then have to go back to twinleaf town to show professer oak then you go back to where yhe guy is blocking the way and he should have gone. hope this helps
to get past the guy blocking the way to sunyshore. you go to mt.cornet and you surf across the water and use rock climb.then there is a cave that go threw. and then theres place that's snowing.
You need to have completed all of the Galatic arc, before you are given access to the Route to Sunyshore. The Route can be found at the Lake Valour Lakefront (where the guy was previously blocking the route), when you first get to Sunyshore, Flint will approach you, he will also tell you where Volkner is (the Lighthouse)
you have 2 beat every single galactic grunt, included those in the galactic building in veilstone city(very important)