It's a once-in-a-lifetime experience.

Meaning

It's a very special and unforgettable experience.

Examples

• John: Are you excited for your trip to Japan?
• Alice: I am! Everyone says it’s <b>a once-in-a-lifetime experience</b>.
• John: I hope you have an incredible time!
• Alice: I'm sure I will! I’ve heard it's truly <b>a once-in-a-lifetime experience</b>.