Tips:
There are hidden doors that make sounds but appear as walls, and fake doors that appear on the map but are not actually real.
If you're stuck, try checking even the objects that might appear more innocuous, like background objects (stones, pots etc.)
You can and should unlock doors even if you can't see them.

Find the hidden treasure that makes a unique star shining sound.

Controls:
Move: WASD
Attack: Left click
Switch to gun: 1
Switch to melee: 2
Close your eyes: E
Unlock a door: R
Interact with object: F
Continue tutorial: ENTER

Credits:
Sound (except 8 bit):
Gentle Wind Gusts | Royalty-free Music - Pixabay
Star shinning | Royalty-free Music - Pixabay
chain rattling (Prison ) | Royalty-free Music - Pixabay
Creaking Gate | Royalty-free Music - Pixabay
Flesh Growing (Horror) | Royalty-free Music - Pixabay

Some 8-bit sounds made using:
jsfxr - 8 bit sound maker and online sfx generator