December 17th was formerly the start of an ancient Roman holiday called Saturnalia. To celebrate, let me post this awesome video by Historia Civilia about it:
Contrary to popular belief, Christmas is not directly derived from Saturnalia, but did adopt some aspects such as gift giving and festivities. Christmas derives its date more from a later Roman holiday named Sol Invictus. Early Christians at that time likened Jesus to the Sun which was venerated in Sol Invictus, hence the connection.
As a Classics nerd, though, I will be celebrating Saturnalia.
Io Saturnalia, one and all.
P.S. I find the Roman god Saturn really fascinating for some reason due to his unusual portfolio, ancient traditions that predate Greek influence, symbolism and such. I keep thinking what a cleric in Dungeons and Dragons would look like worshipping Saturn.