Caves & Cliffs: Part II is currently in development at Mojang as the next major Minecraft update and you can now test the new world generation in a special build.
It's a major change in the method Minecraft is built, and that's why Mojang decided to approach things differently. Minecraft servers Unlike normal testing, this isn't an official Snapshot that you download through the launcher. Instead, if you head to their explainer blog post it gives you some instructions and a download link.
While it's all subject to changes, here's what's different:
New world height and depth - New mountain biomes (lofty peaks or snowcapped peaks meadows, snowy slopes) - New cave generation (cheese, spaghetti, and noodle caves) Local levels of lava and water in the underground - New cave biomes generate naturally underground and within mountains (lush caves and dripstone caves) Natural variation in the shape of terrain and elevation, independent of biomes. For instance forests and deserts may form up on a hill, without needing a special biome just for the purpose of that.