I'm tired of sailing for 10 minutes to get from Point A to B. I may mean that literally!
I'm hoping there's a decent quick travel system. I worry that I've already missed it somewhere, because surely I can't be expected to sail for so long.
Obviously, a direct answer would be a spoiler. Personally, that's okay with me at this point. :P
All the same it's pretty fun!

Use the magic jar on the black swirlies that are on various islands. Shoot out the swirly and it makes a portal to the shadow world, which is an easy way to travel and also a much faster way of waiting for day/night than just standing around.

I discovered it by accident. They I got stick for a minute in the alterworld while trying to figure a way out; just have to press up+attack and you'll get out.

You don't even have to press attack; just press up.