Simple and direct:
* The trip to the Grand Canyon was an unforgettable experience.
* The concert was unforgettable, filled with energy and emotion.
Descriptive:
* The sunset over the ocean created an unforgettable scene of vibrant colors.
* Her kindness left an unforgettable impression on me.
Figurative:
* The story of their love was an unforgettable tale of perseverance and devotion.
* The music filled the room with an unforgettable feeling of joy and hope.
Emphasis:
* That was the most unforgettable moment of my life!
* I will never forget the unforgettable kindness you showed me.
Remember, the best way to use "unforgettable" is to choose a sentence that truly reflects the impact of the experience or event you are describing.