Unforgettable (adjective)

1. Impossible to forget; remaining in one's memory.
2. So remarkable or striking as to be difficult to forget.

Origin:

Un + forgettable.

Examples:

1. The concert was unforgettable, it was one of the best shows I've ever seen.
2. He had an unforgettable experience when he climbed the mountain.
3. The view from the top of the mountain was unforgettable.
4. She had an unforgettable role in the play and received critical acclaim.
5. His speech was unforgettable, it was powerful and moving.