The strongest thing in the game is iron. If you have it, you can hide it inside walls to go quite high. You can also hide raised terrain inside walls to go quite high. I have a many, many floor tower that uses every trick in the book; its in the plains but it goes so high the roof has snow.

No mods. the wider bottom is hidden terrain in the walls. That puts the next narrower level at 'ground', and from there, it goes up with iron as far as I could. I also dug it out to bedrock and flattened it, so it has a very deep basement. I like 3M walls inside, I think it has close to 15 floors, been a while since this one... Also when stone goes red, you can pile wood on another 2-3 floors.
https://steamcommunity.com/sharedfiles/filedetails/?id=2799499765