Sometime in the 1800s there was a great cataclysm.  Not sure if it was natural or manmade but in any case, it was a great mudflood that engulfed cities with magnificent buildings.   Some of these buildings were excavated and restored and exposed  (Expositions)  in World Fairs around the world.  To see some of the buildings, here is a list of World Fairs around the world.

This one was in San Francisco in 1894.  Mid Winter Fair in Golden Gate park San Francisco.

more images of buildings from the Midwinter Fair (1894) San Francisco

This one was also in San Francisco in 1915 in the Embarcadero area in 1915

more images of buildings from the Panama Pacific exposition

Most of the buildings were torn down but some buildings still remain.  In California, Balboa Park in San Diego still remains.

We will be visiting this one in May.  Not at grand as the ones in San Francisco but close enough.