The Undergarden Mod
Want a cool earth like dimension full of monsters and secrets? well tryThe Undergarden! it's a massive world hidden deep below bedrock that you can only enter via a stone brick portal. You will also need to craft a Catalyst in order to activate the portal. Once in you’ll be dropped into a strange and sometimes hostile, but overall beautiful, realm. There are particles floating around almost every step you take and they change depending on which of the 9 new biomes you travel through. You’ll also come across vast forests of new trees and thus new materials to build with. Each new forest is vastly different in color but blends incredibly well between biomes. And of course this mod introduces a hefty amount of new mobs both hostile and friendly, as well as small and very large.
Follow the procedures described below to install this mod into your game
1) Install the Forge
2) Download the mod
3) Put in mods folder