Our otherworld is pretty much infinite, access to basically any world, any universe, multiverse. It's also not a headspace or an innerworld per say, just another world, hence the term 'otherworld'
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One of the most visited, oldest, and most well-known--in the system- places in our otherworld, the Chatterbox.
Essentially, the chatterbox is a multiverse.. of multiverses. Its a big (understatement) cube in a void of sorts, on the cube there are doors. An infinite amount of doors. The doors are not visibly connected to anything like a wall, just standing on their own. They each contain a multiverse, of a fandom. Which multiverse/fandom a door contains is determined by the label on top of each door.
The Key Guards, beings who hold keys to the doors to unlock or lock, may have their own door to contain their creations and such if they want.