Landmark and Magnum opus

Landmark noun - A point in a chain of events at which an important change (as in one's fortunes) occurs.

Magnum opus and landmark are semantically related. in masterpiece topic. In some cases you can use "Magnum opus" instead a noun "Landmark".

Magnum opus noun - Something (as a work of art) that is a great achievement and often its creator's greatest achievement.

Landmark and magnum opus are semantically related. Sometimes you can use "Landmark" instead a noun phrase "Magnum opus".