The Meaning of Life, the Universe, and Everything.
There was this one mod long ago that changed the way Minecraft's worlds worked...
Basically, it allows you to dig way beyond the limit of the world: digging straight down would now eventually lead to The Nether, and digging even deeper would lead you to the supposed other side of the world, back to the surface where'd you'd be flipped upside so you can walk there. It also included a new world type where it'd have that other side right above the normal surface too...
Does anyone here know the mod I'm talking about?? I swear this was a mod that existed, and I wanna find it again.