The nether is a hell like dimension and biome that is linked to the overworld via nether portals.
Nether roof height.
The nether was added as part of java edition alpha s 1 2 0 halloween update and exists as a completely different world from the overworld.
To access the nether the player must construct a nether portal in the overworld portals created in the end do not activate.
Once the frame is built it can then be activated by placing fire within the frame using flint and steel fire charge.
Take obsidian and a flint steel with you to make a nether portal in order to return from the nether roof.
Build another nether portal at least 16 blocks away and use it to travel back to the overworld.
The nether roof needs to be raised to 256 the build height limit.
Now the upper portal should link to the nether roof and the lower one should take you to the actual nether.
To conquer this use non spawnable blocks like slabs torches signs or carpet to mark the way.
This portal should spawn at the nether ceiling breaking some more of the bedrock.
Repeat this to break more bedrock.
Break the nether portal that brought the player to the nether.
It is filled with rugged terrain fire seas of lava columns of lava netherrack unique ores and unique hostile mobs.
Go back to the original portal and use it to go back to the nether.
To create the portal the player must first build a rectangular obsidian frame ranging in size from a minimum of 4 5 to a maximum of 23 23.
Get back from the nether.
This isn t just needed as something that would make gameplay better like making bigger and better caverns dungeons and mobs it s actually harmful to allow the nether roof to exist under the building limit.