This study analyzes the design process of architect Kiyonori Kikutake for the Aquapolis structure, and the design process of manga artist Osamu Tezuka for the exhibition space within Aquapolis based on sketches by Kikutake and interviews with the people involved. The results reveal that 1) Aquapolis was huge compared to the oil rigs of the 1970s, 2) Kikutake was inspired by ancient Greek temples and the arches of Japanese Shinto shrines when he considered the design of Aquapolis, and 3) Tezuka exhibited his concept of a city under the sea with the cooperation of Kikutake.