that actually looks sick how the fuck did you do that all in survival?
With a lot of pickaxes and shovels - There was a little bit of filling in the outside world too.
I originally done with stone tools, then made a diamond pickaxe to get rid of the obsidian and as much stone as possible until it broke. The rest I did with iron tools.
Sadly, just today I realized that the scale of the place is just too damned big for the real world, and attempted to reduce the entire place by 33%. But by doing so it would shift the massive main chamber more to the outside, and that for me is unacceptable.
So I've now decided to leave the place as an elaborate tunnel to Squidbit's dome (I'll restore the front entrance later), and start my project again, at reduced scale, in another nearby mountain location.
Note: There are plenty of chests inside full of cobblestone and stuff, which I plan to eventually use for a pyramid - But feel free to use it for your own projects.
Hopefully the new location will be just as perfect, but for the new reduced size.
I have yet to start digging again.