Yule, Northern Europe
Speaking of pagan traditions that merged with Christian traditions, let's talk about Yule! This Germanic holiday has had more influence on how we celebrate Christmas today than any other. Yule lasted twelve days, and revelers decorated their homes with holly, ivy, mistletoe, and evergreen trees. Burning yule logs (or eating their yummy cake variants) is still a common Christmas tradition. So basically, the easiest way to celebrate Yule is to celebrate Christmas. Pictured: ceremonial burning of a yule log.