Onomichi City Museum of Art sits in Senkoji Park and is known as much for its Tadao Ando redesign as for its modest collection of Japanese, Chinese, and Western art. The building's clean lines make a sharp contrast with the temple paths and hillside lanes around it.
It is an easy addition to the Senkoji Park walk. Go for the architecture, the changing exhibitions, and the views over Onomichi rather than expecting a large city museum.