A glitch occurred in my Minecraft world where an Ancient City spawned inside a mountain in the Deep Dark. Since this glitch can't be easily recreate by using a seed (The glitch has to do with pre-generated structures in the border of rendered areas, then updating the world into the new 1.19.3 generation. It requires to know what version that monument was generated, and render it in a specific way where the new world generation will generate over it), here is the world download.

I found it by buying a cartographer villager's ocean monument map, and got weirded out it led to the middle of a mountain. While digging straight down, I got the fatigue effect, so I had to use tnt instead. I didn't realize it was inside an Ancient City, and got the shit sacred out of once I heard the shrieker going off.

I nearly died, but managed to use some TNT to blast my way out of that maze.