Officially part of Kagawa Prefecture, Naoshima is a small island in the Seto Inland Sea. Though it is a nice rustic getaway from Tokyo, the island is most famous for its numerous modern art museums, architecture, and sculptures. Many of these were designed by the well-known architect Ando Tadao. Some spots to keep an eye out for are the Chichu Art Museum, the Lee Ufan Museum, and the Benesse House.
As you might imagine getting to Naoshima is a royal pain in the, err, backside! You’re going to need to first make your way to either Uno port in Okayama Prefecture or Takamatsu port in Kagawa prefecture before you can catch a ferry out to the island. The ports themselves are hard enough to find let alone the island so plan for a long journey and expect to stay overnight in the area.