>>I'd just like everyone to know that my mind wandered off on a long
>>digression as to which, if any, of the Trinity own the upside-down
>>castle in Cephiro, and how they've decorated it.

>No one owns that or lives there; it's not in Cephiro and it's not even really a >castle so much as a colossal art installation, purpose unknown.

ISTR at least one case of speculation that it was carved from the roots and/or branches of Yggdrasil that penetrated into the world in question... definitely not from a UF story, but an interesting concept nonetheless.