Mordenkainen's magnificent mansion
From Vanathul Wiki
Suggested fluff change:
Will cause a mansion to appear somewhere fitting if possible. A house revealed in a creeping fog, or a new door in an otherwise bare facade. Ideally the fluff is that it does not manifest where it is observed, but rather "slide" in where no one is looking.
The goal is to make it more mystical, cerendipitous and unknowable than just some flashy doorframe.