General:
* Sanctuary
* Refuge
* Shelter
* Asylum
* Safe haven
* Safeguard
* Retreat
* Harbor
* Place of safety
* Place of peace
More specific:
* Harbor (for ships)
* Sanctuary (for animals or persecuted people)
* Refuge (for people escaping danger)
* Oasis (for travelers in a desert)
* Safe haven (for children or vulnerable people)
The best synonym will depend on the specific meaning of "haven" in the context of your sentence.