I added both Floating Castle and Fortress tags to cover all bases when it comes to the structure in the background. I logged into the game to double-check; its the one at the end of Sohr Khai, which has some differences in architecture from Zenith (the one in The Churning Mists). The Duty Finder description refers to all of Sohr Khai as a "palace", while the blurb on the first Encyclopaedia Eorzea about Zenith (page 165) calls it a "fortress".