General synonyms:
* Eternal
* Everlasting
* Immortal
* Enduring
* Permanent
* Classic
* Ageless
* Unchanging
* Unfading
Synonyms emphasizing style or design:
* Fashionable (if it's a style that never goes out of fashion)
* Elegant
* Sophisticated
Synonyms emphasizing value or importance:
* Valuable
* Significant
* Meaningful
More nuanced synonyms:
* Atemporal: This emphasizes the lack of connection to time.
* Epochal: This suggests something of great importance or lasting impact.
* Transcendent: This indicates something that goes beyond time and limitations.
The best synonym for you will depend on the specific situation and what you want to emphasize.