The safe answer
Assume the following:
$MINECRAFTDIR is the path to the Minecraft directory containing your custom data: texture packs, saves, etc.
- Mac OS X:
$WORLDDIR is the name of the world directory (e.g.
The Nether region information is stored in
$MINECRAFTDIR/saves/$WORLDDIR/DIM-1/: if you delete the
region folder within, Minecraft will regenerate the Nether.
The first time you delete it, you might see significant changes (especially after a terrain generation update like 1.8 or 1,9), but if you do nothing and delete it again, you'll notice nothing's changed. That's because the Nether and the real world share the same seed: the first delete just resets the Nether back to its original state (or its new state when the terrain generation code changes) and, since the seed doesn't change, any subsequent deletes do nothing.
So unfortunately, you can't create a completely new Nether while keeping the same regular world intact. But you can at least wipe your Nether clean or have it use the new terrain generation code after a major update.
The Oh-God-You're-Messing-With-The-Forces-Of-Nature answer
It's possible to replace your current world's seed with a new one which, when combined with the instructions above, will create a completely new Nether. I have no idea about the long term implications this will have on your real world, but it should only affect new chunks, not existing ones.
To do this, you'll need a level.dat editor that lets you record and change your current position and export your inventory. I used InvGrid to do this.
Note: this likely awakens the old gods, so be sure to backup your world folders before doing this.
- Create a new world, and either enter a seed or randomly generate a new one.
- Save and quit out of Minecraft.
- Open InvGrid, and select your original world.
- Under the Misc. tab, note your current position (and spawn point, if you want to keep it, although it's not that essential now that you can reset your spawn point with beds)
- Export your inventory, as you'll be wiping it out shortly.
- Save and quit out of InvGrid.
- Use the safe answer instructions to delete your world's Nether region (tee-hee).
- In your world's folder, delete level.dat.
- Copy the level.dat file from the new world you created in step 1 to your curent world's folder.
- Open InvGrid and select your world again.
- Set your position to what you recorded in step 4.
- Import the inventory you exported in step 5.
- Save the world and quit InvGrid.
- Whisper dark incantations and sacrifice whatever live animals you have to appease the old gods.
- Open Minecraft and your world.
You should now have a completely new Nether: at least, it worked on the worlds I tested.