Fraggle Rock: The Bells of Fraggle Rock (1984)
In this Christmas/Solstice themed episode, Gobo questions the utility of their holiday, The Festival of the Bells. He sets out to challenge the myth and find out whether or not the Great Bell actually exists.
There's a surprising amount of existential angst in this episode for a children's show starring puppets.
Meantime, Doc and Sprocket do a bit of exploring of different holiday traditions, and Doc teaches Sprocket about the link between Saturnalia and Christmas in about ten seconds. It's awesome.
There's more than a bit of sappy “look inside for the truth” type stuff by the end, but it really amuses me that not having their festival has actual measurable implications.
Also, I'm a sucker for Fraggles, and a sucker for Solstice-themed holiday episodes. I really enjoy the main song of the episode: “There's a Promise” aka “Raise Your Voices” is fun. And Cantus is in it! What's not to love?