In order to enter this Side Dream you need to interact with the tilted painting inside Uncle Edward room. After that, head to the side dream inside Act 3 (Near the church).
Once Inside Find a big tree (Picnic area) and read the note on the tree left by you uncle.


Now head to the house close to the entrance, go upstairs and interact with the paintings until they are in the correct position, the bookshelf downstairs should be opened showing the first egg
Egg Number 1:

Before heading outside, interact with the painting left upstairs, it will reveal the position of the second egg.
Egg Number 2:
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Next egg will be in a little toilet hut
Egg Number 3:

Next to it you will find some wood benches, look around.
Egg Number 4:
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Continue on until the little river, search at the end of the way.
Egg Number 5:

Enter the next area where you find the picnic with the note for the Easter Egg hunting, look behind the tree.
Egg Number 6:
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Now head to the Moai Monoliths and look near the white cubes

Egg Number 7:

Hunting Completed ! Black Cube unlocked.
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Bonus / Vinyl location: