I've been reading The Children's Book by A.S. Byatt. Very good book, but I was especially struck by the section set in and during the Paris Exhibition of 1900 (think World's Fair), with lush descriptions of the buildings and exhibits.
Thought to take a look on the Flickr Commons pages to see if there were photos from the Exhibition. Turned out there was not only a set of photos, it was a big set (271 photos), and they were even in color! (Hand-colored, but still....)
The full set here.