Dimensional World Mod 1.8, 1.7.10, 1.7.2 is a Mod that adds a complete new Dimension, specially for Mining, but you can do whatever you want to do in it. Just craft some Stone Bricks together with a Pickaxe and you get a special kind of Bricks. They are a little harder to break than normal Stone Bricks and they open you up the ability to visit a new world, the Mining World. Just build a five blocks high and four blocks wide wall with a three by two hole in the middle(same shape as a Nether Portal). Then you need a new Tool to actually create the Portal. Craft a few Stone Bricks, a Flint and Steel and a Stick together to get the Portal Igniter (Portal Multitool). Then right-click the Portal Frames with it and watch, what happens.

Download Dimensional World Mod 1.8, 1.7.10, 1.7.2