The Yule Bell is a large bell that appears in the 2017 Disney featurette Olaf's Frozen Adventure. It is part of an annual tradition for Arendelle in which it is rang by the royal family to signify the beginning of the Christmas holiday season.
King Agnarr and Queen Iduna would ring the Yule Bell every year to let Arendelle know the Christmas season had begun. As Anna and Elsa grew, they accompanied their parents in ringing the bell. However, when the girls were separated and the gates were closed, the bell was put into storage and not rung again for thirteen years.
Role in the short
Several months after Elsa's coronation, winter approaches Arendelle and the bell is brought out of storage to to be rung again. Kristoff and Sven bring the bell into the castle's courtyard, then it is hoisted into position on the castle, with Kristoff guiding it into place. At the stroke of noon, Elsa, Anna, and Olaf then all ring the bell to mark the start of the kingdom's first major Christmas celebration in thirteen years.
After the Arendellians disperse to go home for their own holiday traditions, Anna asks Elsa if their family has any traditions. The only instance that Elsa can recall was the annual ringing of the bell, although Anna points out that the bell was more for the kingdom rather than something personal to their family.