timeless masterpiece; immortal work
Used for works of art, literature, film, etc. that are considered to have lasting value and will be appreciated forever.
This movie is said to be a timeless masterpiece.
His novel has been passed down as an immortal work.
Compound of 不朽 (immortal, unfading) + の (possessive particle) + 名作 (masterpiece). The phrase is a straightforward combination of its parts.