It doesn't have to be a physical entrance. It could be some sort of really powerful drome. They still disappear that way, I think.

The scene where they enter the dreamworld seems like the best reason for it to be physical. If it was something like a drome Tiffany wouldn't have needed to see the gate to enter.

I'll post some of my notes tonight, btw. If I don't forget it again.

Edit: noticed a typo