Riku nodded at that, thinking back to his years of traveling. "It's not exactly forbidden in most of the places I've been," he started simply. "It's just that most people can't manage it. I wouldn't be able to do any if I hadn't met Melificent, she taught me. Just like Sora wouldn't be able to do any without Merlin. Unless, you know, I'd ended up teaching him in the end." Which might not have happened, in all honesty, considering the magic that Riku wielded was mostly based in Darkness, and he didn't want his all-too-optimistic friend having to deal with that sort of thing. Plus, Sora probably didn't even have the ability to use Dark magic.
But at her question he had to think for a moment. "It's sort of both, I guess. There's different ways to get between them. The doors through darkness, but they have to be unlocked, sort of like the seal that brought everyone here, and if you've got a special ship you can fly between them. But most ships can't fly between them, they're not built for that." He'd been thinking about those doors a lot since showing up in Lawrence, and he wasn't entirely convinced that it wasn't the same sort of thing that brought him there. If it was, then the solution would be relatively simple. Find the keyhole. Lock the door. The relatively part came from the fact that this was by far the biggest world he'd been to.