And I'm going to start with the inevitable Osaka Castle.
The present day Main Tower is the third generation. It follows the Main Tower from the Toyotomi period, which was destroyed by fire during the Summer War (1615), and the tower from the Tokugawa period, which was struck by lightning and was burned down.
Another important icon of Osaka city is the Tsuutenkaku Tower (通天閣).
There are a lot of fun attractions, featuring movies like Indiana Jones, Back to the Future, Sesame Street, Shrek, and many many more!