Working in a library, you can find some pretty cool things. There was a day I was reshelving books at the Albertsons Library and found a book simply called On Bullshit. Another day, I found a very old and worn copy of the Masonic Dogma and Morals complete with signatures of past masters who had owned the book. I think the item that I revisited many times was the case book on Roswell.
In Special Collections at Wichita State, I have laid hands on a late 10th century copy of Enchiridion ad Laurentium penned by several different scribes on sheepskin. I perused a sixteenth century copy of The Defense of the Aunswere to the Admonition, Against the Replie of T. C (Thomas Cartwright) penned by John Whitgift. There is a rather large tome from the same century which holds delicate leaves and flowers tucked between the pages.
I own a tiny book. It's a red leather bound copy of Dr. Jekyll and Mr. Hyde, and measures
3 1/4" by 4 1/8" inches.
I never found anything like this, though. Well, that I know of anyway. Such a tiny book!