Though world's fair have long been outmoded, I've always romanticized them. Can you imagine being a Parisian teenager in the late 1800s--wholly interested in technology and science--and stepping onto the grounds of a world's fair? Your head would explode.
We're spoiled these days--what with infinite access to infinite knowledge and all--but back then your mind would have exhausted itself racing with the possibilities of what was taking place before your eyes. Not only had you never seen most of this stuff before, you likely had never even imagined it. The feeling must have been overwhelming.
(Relatedly, check out Erik Larson's The Devil in the White City: Murder, Magic, and Madness at the Fair that Changed America, which chronicles both the production of the 1893 Chicago World's Fair and a serial killer who created a killing chamber in a hotel near the fairgrounds.)