Some fairs come and go, barely leaving a trace that they once existed. Go to New Orleans, for example, and try to find remnants of the 1984 World's Fair. Good luck. Some fairs leave famous structures, such as the Space Needle or Unisphere. The site of Osaka's Expo 70 is marked with the Tower of Sun, the fair's theme symbol.
Here's how the giant statue looked during Expo. It was surrounded by a massive plaza that was topped by a large roof.
After the fair ended most of the complex was removed, leaving the Tower of the Sun standing by itself in a grassy park.
The poor guy looks lonely, so make sure to visit him if you're in the area. You can see some other legacies of Expo 70 as well.