Okamoto’s most notable achievement of the 1970s was his involvement with 1970 Japan World Exposition in Osaka (Expo ’70), for which he designed and produced the central Theme Pavilion, which included a monumental sculpture entitled "Tower of the Sun", an exhibition in and around the tower, and two smaller towers. The distinct appearance of "Tower of the Sun" was influenced by Okamoto’s background in European Surrealism, interest in Mexican art, and Jōmon ceramics"." The pavilion was visited by over 9 million people during Expo ’70, and is preserved today in the Expo Commemoration Park.