The Osaka Aquarium Kaiyukan is an aquarium located in the ward of Minato in Osaka, Osaka Prefecture, Japan, near Osaka Bay. When it first opened, it was the largest public aquarium in the world.

Osaka is a designated city in the Kansai region of Honshu in Japan, and one of the three major cities of Japan (Tokyo-Osaka-Nagoya). It is the capital of and most populous city in Osaka Prefecture, and the third-most populous city in Japan, following the special wards of Tokyo and Yokohama. With a population of 2.7 million in the 2020 census, it is also the largest component of the Keihanshin Metropolitan Area, which is the second-largest metropolitan area in Japan and the 10th-largest urban area in the world with more than 19 million inhabitants.