"Don't Eat the Pictures" is one of Sesame Street's full length feature films. It take place at the Metropolitan Museum of Art and, I think, really captures what the golden age of Sesame Street was all about. The whole gang, including the original human cast, gets locked in the museum overnight. This movie was one of the first appearances of Mr. Snuffleupagus, when he was still considered Big Bird's imaginary friend! The plot also includes a lot of magic/mysticism as Big Bird and Snuffy have to help the ghost of an Egyptian prince break a demon's curse!
Naturally, there's also a ton of great music. Oscar sings an homage to broken Greek busts, and the title comes from a song Cookie Monster sings about wanting to eat mummies. The clip above has my favorite song in it, starting at 0:30. Even as a kid, I knew it would be a lullaby I sang my own child one day.
I really do recommend watching the whole thing, it's pretty sweet. Part 1 is here!