Dear 100 Hour Board,
Is it true there is a great hidden Nephite library full of all sorts of writings and things? I heard this once from a seminary teacher (thus my skepticism) and have been unable to find a quote or anything verifying his words. Thanks for you help.
Your question sounds rather similar to one that posted on the same day that you submitted this question. If you missed it, here is the link http://theboard.byu.edu/?view=&qid=3749.
The cave described in that question is the only thing I can think of that could possibly be described as a "Nephite Library". No specific mention was made of where the plates Mormon and Moroni condensed from were then put though it would seem the above mentioned cave is a distinct possibility, regardless of it's actual location. In the previous question and answer that I referred you to and in other places I have seen referencing it, they refer to it as a vision. However, the only account I could find of it does not seem to be a vision. The account is in the Journal of Discourses, full reference at the end of the excerpt.
Brigham Young, on June 17, 1877, related the following: "I lived right in the country where the plates were found from which the Book of Mormon was translated, and I know a great many things pertaining to that country. I believe I will take the liberty to tell you of another circumstance that will be as marvelous as anything can be. This is an incident in the life of Oliver Cowdery, that he did not take the liberty of telling such things in meeting as I take.
"I tell these things to you, and I have a motive for doing so. I want to carry them to the ears of my brethren and sisters, and to the children also, that they may grow to an understanding of some things that seem to be entirely hidden from the human family. Oliver Cowdery went with the Prophet Joseph when he deposited these plates. Joseph did not translated all of the plates; there was a portion of them sealed, which you can learn from the Book of Doctrine and Covenants. When Joseph got the plates, the angel instructed him to carry them back to the Hill Cumorah, which he did.
"Oliver says that when Joseph and Oliver went there, the hill opened, and they walked into a cave, in which there was a large and spacious room. He says he did not think, at the time, whether they had the light of the sun or artificial light, but that it was just as light as day. They laid the plates on a table; it was a large table that stood in the room. Under this table there was a pile of plates as much as two feet high, and there were altogether in this room more plates than probably many wagon loads; they were piled up in corners and along the walls.
"The first time they went there the sword of Laban hung upon the wall; but when they went again it had been taken down and laid upon the table across the gold plates; it was unsheathed, and on it was written these words: 'This sword will never be sheathed again until the kingdoms of this world become the kingdom of our God and his Christ." I tell you this is coming not only from Oliver Cowdery, but others who were familiar with it, and who understood it... I take the liberty of referring to those things so they will not be forgotten and lost." (19 Journal of Discourses 38)