Odaiba (お台場) is a large artificial island in Tokyo Bay, Japan, across the Rainbow Bridge from central Tokyo. It was initially built for defensive purposes in the 1850s, dramatically expanded during the late 20th century as a seaport district, and has developed since the 1990s as a major commercial, residential and leisure area. Odaiba, along with Minato Mirai 21 in Yokohama, is among a few manmade seashores in Tokyo Bay where the waterfront is accessible, and not blocked by industry and harbor areas. For artificial sand beaches in the bay, Sea Park in Kanazawa-ku is suitable for swimming, Odaiba has one, and there are two in Kasai Rinkai Park area looking over to the Tokyo Disneyland. Daiba (台場) formally refers to one district of the island development in Minato Ward. Shintaro Ishihara used Odaiba to refer to the entire Tokyo Waterfront Secondary City Center (東京臨海副都心, Tōkyō Rinkai Fukutoshin) which includes the Ariake and Aomi districts of Kōtō Ward and the Higashi-Yashio district of Shinagawa Ward.