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

Meaning

It was a very special and memorable experience.

Examples

• John: 'My trip to the Amazon rainforest was incredible.'
• Alice: '<b>It was a once-in-a-lifetime experience</b>, I'm sure.'
• John: 'Yes, <b>it was a once-in-a-lifetime experience</b>.'
• Alice: 'Seeing the Northern Lights was breathtaking.'