I could see the Yellow Brick Road being a portal, but it is hard to know until the writers reveal more of their plans. They might be changing a lot in their storytelling for next mini-season, knowing the ratings did not improve and Wonderland tanked.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass