Sure, the Amazon Kindle might have dynamic font adjustments, and it can hold thousands of books, but can it do this? Printed in the late 16th century this small book from the National Library of Sweden is an example of sixfold dos-à-dos binding, where six books are conjoined into a single publication but can be read individually with the help of six perfectly placed clasps. This particular book was printed in Germany and like almost all books at the time is a religious devotional text. The National Library of Sweden has a fantastic photo collection of historical and rare books where you can find many more gems like this, and this, and this.
Update: And if you really like amazing old book discoveries, you should be following Erik Kwakkel, the Medieval book historian at Leiden University in the Netherlands, who originally unearthed this story. (via Neatorama)