There are many synonyms for "unfamiliar," depending on the context and nuance you want to convey. Here are some options, categorized by meaning:

General unfamiliarity:

* Strange

* Unknown

* New

* Unaccustomed

* Foreign

* Uncommon

* Exotic

* Unrecognized

* Alien

* Novel

* Untried

Unfamiliarity with a specific thing:

* Unacquainted (with something)

* Unversed (in something)

* Ignorant (of something)

* Unskilled (in something)

* Unpracticed (in something)

Unfamiliarity with a person or place:

* Strange

* Unwelcoming

* Inhospitable

* Hostile (extreme case)

* Unfriendly

Unfamiliarity due to lack of knowledge or experience:

* Naive

* Unsophisticated

* Novice

* Amateur

The best synonym will depend on the specific situation and the desired tone.