General:
* Silent
* Still
* Peaceful
* Tranquil
* Serene
* Calm
* Hush
* Soundless
* Muted
* Undisturbed
* Reposeful
More specific:
* Discreet: Suggesting caution or secrecy.
* Secretive: Implying concealment or hiddenness.
* Subdued: A feeling of being restrained or toned down.
* Solitary: Alone or isolated.
* Unassuming: Not drawing attention to oneself.
Figurative:
* Whispering: Very faint or low-key.
* Hushed: A sense of awe or reverence.
The best synonym for "quiet" depends on the specific situation and the tone you want to convey.