Brain Snacks: Tasty Tidbits of Knowledge
Daniel switches the language it's written in. Chapters 2 through 7 are written in Aramaic, the others are written in Hebrew. (Source)
According to the time frame provided by the book, Daniel would've been 82 years old when he was thrown into the lions' den. (Source)
People have tried to argue that Darius is actually another name for the famous Persian Emperor, Cyrus the Great (though he might've been a ruler of Babylon who paid tribute to Cyrus). The argument for Darius being the same as Cyrus is actually a pretty good one: the Hebrew authors might've considered Medes and Persians to be basically the same, and there may have been a copyist's error when translating the name "Cyrus." Or the Emperor may have even had different titles. (Source)