South Park: Season 2, Episode 7

2 - 7: City on the Edge of Forever (a.k.a. Flashbacks)

During a snowy bus ride, Mrs. Crabtree loses control of the bus and it ends up on the edge of a cliff. When she leaves in search of help, the children are still trapped on the bus, and they remember some of their past adventures. Mr. Mackey tries to deal with the parents who are upset that their kids are missing.