The One question to rule them all!!!- or not as the case may be.

There is one thing i'd like to know more than
anything else about Tolkien's world, which i can't find the answer to. I
was hoping you guys or gals could help me.
The question is- If Middle Earth is part of
a great land, then what are the other parts? I know about Beleriand and
Middle- Earth, but what about the rest of the country, and what is the
other side of the Great Sea? And could someone describe the Undying lands, and why all the Elves go there?

I would really appreciate it if you help me with this, and i can't find
the answer to this, but then again i haven't read the history of Middle-
Earth, so there may be an answer. I can't seem to find any maps of other places other than Beleriand and Middle- Earth. If anyone knows where i can find any, please could you give me the URL if it's online?