How to get all achievements in Monument Valley 3
Botanist
In the 3rd level, The Hidden Fens, you will unlock access to a boat. Once you get on a boat, you can steer it into white lily pads in the water. There will be 8 little blue bulbs on some of these lily pads… 2 in the first grouping, then 3 and 3 in later groupings. Run the boat into these 8 little blue bulbs to open the flowers and unlock the achievement.
Dance Party & A Relaxing Break
After you complete level 3, The Hidden Fens, you will get off the boat at the lighthouse. A cutscene will play and a lady in yellow will appear in the lower right. Interact with her to get some plot. Interact with her a second time to dance and get the Dance Party achievement.
Immediately after that, click next to the child reading a book in the same scene. You will walk next to the child, sit down, and read a book of your own next to them and get the A Relaxing Break achievement.
Break Lucie and Todd’s Hearts
Click the dot in the upper left, then the dot in the upper middle to open the Settings. Then click on Preferences. Then on OFF for Audio and you’ll get the Break Lucie and Todd’s Hearts achievement.
Metamorphosis
After you complete the game, enter the lighthouse and earn the Metamorphosis achievement.
The Rest
The other 10 achievements are story-related, for completing each chapter. They can not be missed!