The ExtraTERRORestrial Alien Encounter (often abbreviated Alien Encounter) is a "theater-in-the-round" attraction located in the Tomorrowland section of Disneyland Resort and (formerly) in the Magic Kingdom theme park at Walt Disney World Resort. A co-production between Walt Disney Imagineering and Lucasfilm, the attraction is a darkly humorous science-fiction experience that uses binaural sound to achieve many of its effects. A warning outside the attraction's entrance alerts guests that it is intense and not intended for children under the age of 12, however its height requirement was just 48" for guests.

It opened briefly for previews on November 29, 1994 in Disneyland and on December 16, 1994, in Walt Disney World on the site of the former Mission to Mars attractions in each park, but were ordered closed on January 12, 1995 for retooling by then-Disney CEO Michael Eisner, who deemed it was not intense enough. These two rides opened officially on June 20, 1995 as part of the Disneyland's and Magic Kingdom's New Tomorrowland renovation. Upon it's opening, some Disney fans praised ExtraTERRORestrial Alien Encounter for its darker tone in contrast to other attractions at Magic Kingdom. The Florida version of the ride closed permanently on October 12, 2003. The attraction in Walt Disney World was replaced by Stitch's Great Escape!, which opened on November 16, 2004. It used much of the same technology and set pieces from its predecessor, but was hated by many fans and critics alike that it finally closed on 2017 without any official announcement and it sits abandoned rotting over time.

However, the California version in Disneyland is still operating and going strong due to popular reception and people listening and knowing the warnings of the intensity of the ride, which the people in Florida didn't in the Walt Disney World version.

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