I read one similar short story, long ago, can't remember the title. The main character delves into an artificial "planet" with inhabited layers and forgotten technology, guided by a talking "magic" artifact until reaching a zero-g core. The inner layers were lit with "skymoss" that lit and faded to simulate a day-night cycle. That's about all I recall, really.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort