Kingdom Hearts 2 Gate Opening?

Alright, so today I decided to go buy a used version of KH2. I've beaten the game before, but I was wondering about the gates in the world that never was. Is there any way that you can open the gates up?Or are they just there for looks?

That's the one!

Itt's been a long time since I played it, but don't you just go into whichever one is active? Right now this seems like something you should have referred to a walkthrough for, unless if there's something I missed that wasn't clear.

I have beaten the story and stuff, but is there a way to activate the gates?