Izu Peninsula, Shizuoka
The Izu Shichito (seven islands) Islands, floating on the Pacific Ocean south of Sagami Bay, are a group of volcanic islands in the Fuji Volcanic Belt that stretches from north to south for about 540 kilometers. The group consists of O-shima, To-shima, Nii-jima, Kozu-shima, Miyake-jima, Mikura-jima and Hachijo-jima islands, and is a part of Fuji Hakone Izu National Park. When Aoga-shima Island and other small islands are included, the entire collection is called the Izu Islands, and it is administratively a part of Tokyo. With such diverse marine life, Izu has become a prime locale for divers looking for one of the world's best-kept diving secrets.
More info: https://www.jnto.go.jp/eng/location/regional/tokyo/izusititou.html