Atmospheric Nether (Datapack)

The datapack expands the Nether's terrain so that exploration covers more ground. Deeper layers receive Overworld-style cave generation, with large smooth caves that connect through noodle-style spaghetti caves into wide networks. Entrance caves open at random points near the surface, and some of them are sealed past the edges of the continents.

It adds 27 biomes in total: 7 forest biomes, 9 cave biomes, 5 subterranean river biomes and 6 other surface biomes. The bedrock floor and ceiling are extended upward and downward, leaving room above the Nether roof. Vanilla ancient debris heights stay unchanged, while one biome spawns the ore more often in larger clusters.

Because the mod alters the Nether's generation, it should be applied to a world before that area is generated. The author recommends pregenerating the Nether to the desired distance, since generation is slow and uses a considerable amount of RAM. The datapack is published for Fabric, Forge, NeoForge and Quilt and needs a server that runs it, while clients can join without installing it.