due west
Refers to the exact cardinal direction west, as opposed to a general western area.
この窓は真西を向いている。
This window faces due west.
真西に進むと海に出る。
If you go due west, you'll reach the sea.
Compound of 真 (ma, 'true') + 西 (nishi, 'west'). The prefix 真 is used to indicate exactness in direction words.