How one thing leads on to the next. . . I started with considering the economics.  A mountain fastness without much arable land would need to be supported. . . which led me to think about whether the countries it was protecting would support it. . . and although there were only two of them at that point, I pondered on. . . .

And up popped this cranky, irascible wizard who first created it. 

Never to appear in the story, only its backstory.  Nevertheless, he carefully crafted it to warp the paths and ways leading from the dangerous lands to the others, so that they went to a choke point, and those who supported it were defended by it.  Quite a cranky fellow.  Would have set it up to avoid any chance of their being left off.  Which instantly had another character, in the story, making note of a failure and readying knights to send off there and ward off the evil they had let in. . .

But minutes after that, the muse observed that the wizard's spell not only twisted the paths, it also affected the castle.  Which seems Euclidean, most of the time.  Indeed, it's only when you turn your back on it that you are in danger of its changing.  To adapt itself to your new needs  In its opinion.  Though at the moment it's all convenient to the heroine, once she gets over how it's also creepy.  (Hmm.  prods muse.  Should consider whether it will alos inconvenience her.)  It can, for instance, expand or even add a walled garden.

(Thus far, nothing about clothes, except that some cultures wear more expensive ones, and more jewelry.  0:)