20. Back to The Future Part 3 (1990)
Where Do They Start? Specifically, in this film, 1955. However, Marty McFly (Michael J. Fox) has done a lot of time-travelling by this point.
Where Do They End Up? 1885, where Doc Brown (Christopher Lloyd) is stuck.
Biggest Culture Clash: Marty adopts the non de plume of Clint Eastwood to get by.
Unresolved Paradox: If Doc Brown got stuck in 1885, and left his DeLorean for Marty to travel back to rescue him, that means there must be two DeLoreans in the Wild West now.