A house almost a 100 years old, with one of the best view of Onomichi, nice fluent English speaking staff, a cafe for evening cultural exchange.
I would say the only "problem" is that it is up the hill, but that is not really a problem, rather one of the reasons to stay there. I had to climb up the stairs, and always was out of my breath and sweating (it was in July). but it is worth.
I recommend to arrive in a time when the cable car is still working (this way you only have to go down), or to give it a lot of time, going not strait up, but just wandering around the hill side, eventually getting to the guesthouse.
BUT, it is not open before 15:00, you might not be able to even put down your bags, so be sure to arrive after opening time.
(other services include washing and drying machine, Wifi, towel borrowing, etc)
Definitely will go back another time.