Full list of all 16 Monument Valley 2: Panoramic Edition achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Looks like you found an Easter Egg
Completed Prelude
Completed The Vestibule
Completed The Oasis
Completed The Viaduct
Completed The Archipelago
Completed The Docks
Completed The Towers
Completed Aphelion
Completed Mén-An-Tol
Completed The Botanical Gardens
Completed The Lyceum
Completed The Orchard
Completed The Sunken City
Completed Mirador
Completed Lost Forest