Using public transport for getting to Okunoshima by train and ferry is easy from Hiroshima or Okayama. Coming from Shikoku, travel by car or bicycle is recommended.
Okunoshima is a short ferry ride from Hiroshima's Mihara city. Take a Shinkansen bullet train (not Nozomi) from Okayama or Hiroshima to Mihara station (26-40 minutes). On weekends, a high speed ferry runs 5 times a day from the port near Mihara station. On weekdays, take a local train on the Kure line towards Hiroshima. Get off at the third stop (Tadanoumi). Ferries to Okunoshima run regularly from the port near the station.
Coming from Shikoku, take the Shimanami Kaido sea road from Imabari city to Omishima island. Follow the coast to Sakariko port for the short ferry ride to Okunoshima.