In 1999, The Matrix changed everything. The sci-fi epic from sibling directors The Wachowskis starred Keanu Reeves as a hacker named Neo who discovers that all of humanity is trapped in a simulated reality and secretly controlled by a system of artificial intelligence. Its wildly imaginative cinematic world was as groundbreaking as it was complex. So, too, were the film's dazzling and action-packed set pieces, which blended martial arts with cutting-edge special effects (how many subsequent films ripped off the slowed-down "bullet time" concept?). On the 20th anniversary of the film's release, we take a look at some mind-blowing behind-the-scenes photos that show just how the Wachowskis pulled off the movie that would have a lasting effect pop culture forever.