There's not really much to know. It's the Netherworld, home of demons, dark energy, big nasty monsters... stuff like that. Usually, if there's too much darkness back home, gates will pop up and demons would come out. We used to go down here to train but...

This place is new, though. Don't ever recall ending up in a castle... with shops and everything... [Nevermind that she didn't even remember stepping through a gate in the first place.]

Usually, there's more gates around and eventually one leads you back to the human world... but I haven't found it yet.

And... err, that's pretty much it?