south side of a mountain; Sanyo district
The literal meaning is 'south side of a mountain', but in modern usage it almost always refers to the Sanyo region of Japan (southern Honshu along the Seto Inland Sea). The literal sense is rare outside of classical or poetic contexts.
The Sanyo region faces the Seto Inland Sea.
I went to Hiroshima on the Sanyo Shinkansen.