Declaration of Independence at NYPL
Thomas Jefferson made several copies of the Declaration of Independence, and one of these copies is on exhibition at the New York Public Library. And it's free to see it (I ♥ NY). It will be on exhibition to the 5th of August. I might go today.
About three months ago, I watched a special on PBS about the preservation of the original because it was written on pig skin, which is not archival at all. The government spent approximately $5 million on the design and construction of the vault for this document (the show covers this process). There's even some humor. At one point, someone suggested to put tiny silicon pebbles to in several cavities of the case to secure it from moisture, but that notion was rejected over and over again. Anyway, it's worth watching.