Minecraft wiki entry for Nether_hub, associated text: First, you will need to get to the nether roof. There are various different ways of doing this, many of which are listed at Tutorials/Breaking bedrock. Go ahead and break a hole to the nether and put ladders in it with an iron trapdoor on top with a button. Once you have done this, mark the coordinates of the trapdoor so you will always be able to get back there. Now go to an existing portal in the real nether and break it. You may want to relight it later, but for now it will just get in the way. While you are there, mark the x and z coordinates because you will now need to build a portal in that same spot on the nether roof. Use your trapdoor to get back on the roof and travel to the coordinates you just marked. Create a portal there, light it, and step through. You should end up in the overworld at the portal that corresponds to the one you just broke. If you step through again, you should find yourself back on the nether roof. If you don't want mobs spawning on top of the portals, (you probably don't) put slabs or carpet on top to prevent mob spawning. At this point, you have done the minimum and your portal is successfully linked. Repeat for any other portals you have before moving on.