Naught but stone, ice cold water, and Monsters en-masse hunting you down in this forever dark place.

Can you survive and thrive in this place where the sun has never shone?

Underworld makes use of the Nether's terrain to create a massive cave-world that has overtaken the "Overworld".

Underworld uses several tricks to keep it's worldgen as light-weight as possible, sometimes even managing to complete worldgen 25% faster than vanilla!

Underworld also brings (very) few new blocks & items to help:

Hang Vines spawn in the ceiling of this massive cave-system, and are Ore-Dictionaried to vanilla string.
The Brazier is a decorative light-source, but requires flint-and-steel to be smacked on it to light up.
The Lantern is a dynamic light-source to help you as you venture around in the eternal night of Underworld.

Underworld is extremely young, so there will be bugs and issues. Please help by finding them all!

To generate an Underworld map:

SinglePlayer: Just select "Underworld" in the available maps, just like you would select a flat map.

Multiplayer: In the server.properties file, change the line: level-type=DEFAULT to level-type=CAVES, and be sure to delete the level.dat & overworld region files.

0.3.12: Recipes by the Campfire

Updated Mob-Spawning mechanics.
- Squids are now being force-spawned manually.
- Disabling force-spawn for Roots entities.
- More than doubled amount of mobs allowed to co-exist in a 64x128x64 area (7-16).
Updated JEI support to 3.14.7.416.
Added MineTweaker Support for the Metamorphic Table.
- Read here to learn how to add and remove recipes.
Removed the Sugar Pile from the creative tabs. Right-clicking sugar on the ground will still place them.
- Placing the sugar down is vital to the pile's interaction with hostiles. Placing the pile down, directly circumvented it.
Changed how the Sugar Pile's interact with hostile entities.
- Removed the "Fireflies push hostiles away" ability.
- Made Fireflies "daze" hostiles instead. Hostile entities will now freeze in place and watch the Fireflies.
Trimmed the chance for Moss-Stone to spawn, from 5% to 4%.

Source-Code can be found here: https://github.com/Matryoshika/Underworld
Please post issues at mentioned GitHub!