Which 1989 movie has this as it's tagline, "Getting back was only the beginning."?

The 1989 movie with the tagline “Getting back was only the beginning.” is Back to the Future Part II. The line captured the sequel’s central idea: returning home would lead Marty McFly and Doc Brown into an even larger adventure.

Released in November 1989, the film begins soon after the first Back to the Future ends. Marty and Doc travel from 1985 to 2015 to prevent a future crisis involving Marty’s children. Their intervention creates an alternate 1985, forcing Marty to repair the damage while avoiding changes to the original timeline.

The sequel expanded the series’ time-travel structure by moving between 1985, 2015 and an alternate version of 1985. It also revisited the 1955 events from the first film from a different perspective, making continuity and cause-and-effect central to the story.

Back to the Future Part II was followed by Back to the Future Part III in 1990. The two sequels were filmed partly as one extended production, but Part II remains the film associated with this tagline and its memorable vision of the future.