Done with this book? No need to get another one, because you can just open it a different way to reveal another book. Done with that one? Well, just open it another way and you'll have another story. And again. And again. Until you do it six times. Because, you see, there are six books in this one book. It just depends how you open it.
This book, which was bound in the late 16th century, is filled with German text and is owned by the National Library of Sweden. It's like a dos-à-dos book (two books that share the same binding, back to back) but with even more secrets in 'one' binding. Erik Kwakkel says:
They are all devotional texts printed in Germany during the 1550s and 1570s (including Martin Luther, Der kleine Catechismus) and each one is closed with its own tiny clasp. While it may have been difficult to keep track of a particular text's location, a book you can open in six different ways is quite the display of craftsmanship.
You can see more pictures of the 6-in-1 book here. It's like a very limited, very old Kindle that could only hold six books.