The CubeWorld mod for 1.7.4 breaks up your world into glass cubes. Each cube has a separate biome inside, complete with mobs and dungeons. If you travel to the Nether you will also find that the area is broken up into cubes, and even glowstone is in its own cube.
Download the CubeWorld Mod for 1.7.4:
CubeWorld Mod for 1.7.4
Go to %appdata%/.minecraft/versions.
You should see a folder named 1.7.2. Make a copy of it, and rename the copy to Cube_World_1.7.2.
Inside the new folder, you should see a file called 1.7.2.jar. Rename it to Cube_World_1.7.2.jar.
Inside the new folder, you should also see a file called...