Was just getting my head around the “Middle of the night”, but of course it was . :)
Have been there twice and never twiged on to it being hollow. But it is a special place to visit.
We like to entertain ourselves with the quaint notion that our "Habitats", including the Flying Castle of course, constitute a tiny world, with its own time zones, but only enough room for three of them.
Accordingly, if you wake up in the middle of the night, and are indisposed to sleep, a quick tube ride will bring you to an adjacent Habitat, where it is the middle of the day.
By this process, we don't have "morning people" and "night people". We just have mobile people, and cafes and restaurants to serve them whatever they fancy.
Coffee, for me, please. Hold the adulterants.