It was a once-in-a-lifetime experience.

Meaning

The experience was unique and unlikely to be repeated.

Examples

• John: Traveling to Japan was amazing!
• Alice: I bet! <b>It was a once-in-a-lifetime experience</b>, wasn't it?
• John: Absolutely! <b>It was a once-in-a-lifetime experience</b>. I'll never forget it.
• Alice: You should definitely go back someday!