unvergesslich
unforgettable
So impressive, beautiful, or meaningful that it stays in one's memory for a long time and is not forgotten.
Unsere Reise nach Italien war ein unvergessliches Erlebnis.
Our trip to Italy was an unforgettable experience.

unforgettable
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unforgettable
So impressive, beautiful, or meaningful that it stays in one's memory for a long time and is not forgotten.
Unsere Reise nach Italien war ein unvergessliches Erlebnis.
Our trip to Italy was an unforgettable experience.

The word is made up of three parts: the prefix 'un-' means 'not', the stem comes from 'vergessen' (to forget), and the ending '-lich' makes it an adjective. So 'unvergesslich' (unforgettable) literally means 'not to be forgotten'.
Der Sonnenuntergang in den Bergen war einfach unvergesslich.
The sunset in the mountains was simply unforgettable.
This adjective is very often used to describe positive experiences. Common combinations are 'ein unvergesslicher Moment' (an unforgettable moment), 'ein unvergesslicher Urlaub' (an unforgettable vacation), or 'eine unvergessliche Begegnung' (an unforgettable encounter).
Das Konzert war ein unvergesslicher Abend für alle Fans.
The concert was an unforgettable evening for all the fans.
A very typical sentence construction is the combination with the verb 'bleiben' (to remain). This expresses that a memory stays permanently in one's mind.
Diese Reise wird mir für immer unvergesslich bleiben.
This trip will remain unforgettable to me forever.
legendary
'legendär' and 'unvergesslich' can both describe that something was very special and stays in your memory for a long time. 'unvergesslich' is more direct and more neutral: it mainly says that you do not forget something, for example a beautiful day or an important experience. 'legendär' sounds stronger and often more informal. It means not only that something stays in memory, but also that it was extraordinary and perhaps many people talk about it. For personal memories, 'unvergesslich' is often more natural; for big, famous, or especially successful events, 'legendär' fits well.

Der Urlaub mit meiner Familie bleibt für mich unvergesslich.
The vacation with my family remains unforgettable for me.
Das Konzert im alten Stadion war legendär.
The concert in the old stadium was legendary.