Shimanami Kaito (recommended) + Kirosan Observatory

Great biking trail leading over six Islands from Shikoku to Honshu connected by suspension bridges (including  Kurushima-Kaikyō Bridge, the world's longest series of suspension bridges, see picture). Bike pick-up at Station 13 close to JR Imabari and drop-off at Station 1 in Onomichi. Including many breaks to take pictures, lunch and other refreshment pauses it took 9,5 hours on a citybike. Kirosan Observatory is worth the detour if the weather is nice. If it is too overcast, consider going up Shiratakyama Observation Deck instead, it is only 181m high instead of 307m.