The Mines gardening achievement.

[hottabych91]

If you try to plant something in the Mines, it will be destroyed once you re-enter the level (as it will be regenerated). But you could receive the achievement like "Would it grow here?"
Just an easter idea, because I know that some youtubers tried it: https://www.youtube.com/shorts/WtZLXQjH7PA?feature=share

 

[FilthyGorilla]

Stardew doesn't really have any easter egg achievements though I could see an expansion of achievements, we just got some for the first time in years alongside 1.6

 

[Lew Zealand]

Was Fector's Challenge an easter egg achievement or just a hidden one? I dunno what the difference is really.