Lonely Planet has named the Shimanami Kaido as one of fifty 'Epic Rides' worldwide. It's only 70km long (although there are lots of interesting side trips) so it can't be considered as a 'tour' in anybody's book. However, it can certainly form part of a great tour around the western and southern portions of Japan.
Shimanami Kaido cycling route makes world top 50 list?The Asahi Shimbun