The Pocket Portals Mod allows you to make a separate world inside your local save. You make the portal out of dirt and a dirty stick which is made from 1 dirt block. The other world is made completely out of barrier blocks but you can craft a pickaxe for that (you won't get the blocks when you break them). For more info go to https://www.youtube.com/watch?v=ya6SgPSiNz0&feature=youtu.be . The pickaxe is a W.I.P.
