Today, we are looking at how you enter the Methyr. Now I don't know very much about how you get to the Methyr, except this :

There are naturally spawning methyr portal dungeons. Go in one, and collect the book inside. There is then a room with 4 beams and 5 blocks that are foreign to vanilla minecraft. Somehow, you use the book and this room, to open the portal, and then you're in the Methyr, the mountain dimension.