What's the Name of That Book??? discussion

I first read the book in 2012, it wasn't new at the time I believe. It was about a boy (I think?) who lived in a world built on a rock with steep cliff ledges that nobody had ever climbed to the very bottom of. There was some sort of mystery surrounding the creation of the rock world, and the Earth and civilization that came before it. I think that at some point in the book, the boy travels underground, inside the floating rock. The book had a few sketches of the world included, and there might have been a journal from someone who knew the old Earth, and the boy's first hints were from that.

Journey Outside?

Still looking, Sun?

Could this be a book from the Edge Chronicles by Paul Stewart?

The Curse of the Gloamglozer for Audrey's suggestion.

On by Adam Roberts?

(view spoiler)[The world is actually Earth, but gravity started working sideways after a physics experiment went really, really wrong, so everything's either hanging on or falling round. (hide spoiler)]

SPOILERS:
I remember this book... trying to find it now. There were three tiers, and he climbed up to the top level first and then at the end down to the bottom level. I remember he lost a finger while climbing down. Currently annoyed that I can't find this in my read list!

If not one of the suggestions above, maybe The House of Power?

Oh, The House of Power, I think that's the one!

Here's the Google Books preview of The House of Power by Patrick Carman- Ayshe and Hermitqueen's suggestion:

https://books.google.com/books?id=_AQ... There are different cover images.

"And to the very bottom - to the Flatlands - you climbed down there as well?" "I did," answered Edgar. It seemed that word of his adventures had spread. "I don't believe you," grumbled the man. And he didn't.

This is more fantasy than sci-fi, but Beyond the Deepwoods?

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Sun, your book does sound like Ayshe and Hermitqueen's suggestion of The House of Power by Patrick Carman.

Matches: Floating rock world [with 3 levels], steep cliff ledges, nobody climbed to the bottom, creation is a mystery, boy travels underground, journal from someone who knew old Earth.

+ Water is scarce, people eat figs & rabbits, girl with slingshot
+ Boy (main character) lives on the middle level, he works harvesting figs, excellent climber, mischievous