Sliding Doors + Mastermind of Design

Discussion s/b in Trivia. Were the hortizontal and verticle Door Shifting real or were they Movie Magic? If real, please discuss the mechanics, beauty, problems, time building, & costs for this effect. It's truely amazing. To make that happen, there s/b ceiling or floor tracks but none appear.....it's all done very asthetically. How? Amazing feature. ? ?