During the Thirty Years' War, the Prague Castle was occupied by the Swedes, who later removed all the valuables and took them back to Sweden. When people visit the Prague castle today, they notice it is surprisingly barren, which is for this reason. Some of those valuable artifacts that the Swedes looted are now on display in the Drottningholm Palace over there.
One of the more peculiar items they took was the Codex Gigas– or the Devil's Bible. This mysterious book is the largest handwritten book in the world. Consensus is that the book was writtend sometime in the beginning of the 13th century. It made its way to the Cistercian monastary in Sedlec near Kutná Hora, then was bought by the Benedictines of Břevnov monastery in Prague. Rudolf II, who had been fascinated by the codex as a little boy, purchased the book as an adult.
Legend is that the author of the codex was a corrupted monk who made a deal with the devil. The monk had broken his vows and was sentenced to be walled in ALIVE! He made a bargain with the clergy that he would write a book for them in one night if they would spare him his punishment. The church obliged.
This may have been a greater undertaking than the monk had expected. Although he wrote as fast as he could, by midnight he realized this was a loss cause. Distressed, he prayed to the only one who would listen to him– the Devil. In exchange for his soul, the monk was able to write a book that was 92 cm high, 50 cm wide and 22 cm thick. In gratitude, the monk drew a picture of the Devil on the book– this feature that gives the codex its nickname.
Medeival legend asside, experts estimate that it would've taken 20-30 years to write. Despite it's satanic reputation, the book has survived.