Java Edition:Nether Terrain in the Overworld
When the Nether was first being developed in Minecraft Alpha, it wasn't added to multiplayer in the same way as it was in singleplayer due to a lack of necessary networking code. Instead of Nether portals, a new setting was added to the server properties called hellworld that, when enabled, would make a server load its world as the Nether instead of the Overworld.
Obtaining
Alpha Server
Alpha server 0.2.2 added the server property hellworld=false to the server.properties file. By changing this to hellworld=true, every newly generated chunk will generate with nether terrain, the nether fog will be present, and all biomes in the world will be loaded as hell, due to biomes not being saved until release 1.2. This means that one should take caution as Nether mobs, especially ghasts, can spawn in old chunks. After either setting hellworld=false or updating beyond this range, the hell biome will be lost, but all Nether mobs and terrain will remain. It is also possible to generate the Nether farlands.
World Save Insertion
Gallery
New Nether generation on the border of older Overworld generation.
