I’m reading this thread with interest. My experience of the seto instant sea is limited but I found it to be one of the most beautiful places I’ve been.

Only got to do a day trip. From hiroshima to takehara on a joyful train (it had portholes). Takehara has an edo period old town and a couple of sake breweries. Then a short ferry ride across to Osakikamijima, a taxi to the ferry to aki tsu and back on the train. Absolutely delightful.