Caves & Cliffs: Part II is in development at Mojang as the next major Minecraft upgrade and you can now test the new world generation is a special build.
It's a huge change to the way the world is created in Minecraft, so Mojang decided to do things a little differently this time. Unlike normal testing, this is not a Snapshot you download in the launcher. Instead, if you head to their explainer blog post it gives you some instructions and a download link.
Although it's all subject to change, here's what's different:
- New world height and depth
- New mountain biomes (lofty peaks, snowcapped peaks, grove, meadow, and snowy slopes)
- New cave generation (cheese, spaghetti, and noodle caves)
- Local water levels and lava levels in the underground
- New cave biomes generate naturally underground and inside mountains (lush caves, dripstone caves)
- Natural variation in terrain shape and elevation, independently from biomes. For example, forests and deserts could form up on a hill without needing a special biome just for that.
- New ore distribution (see this chart)
- Large ore veins
- Integrated mountains, caves, and cave entrances
- Monsters will only spawn in complete darkness
Once they get it all fixed up nicely, it should make the Minecraft world quite a lot more interesting.