The sealed envelope

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Hint 1: Access to the places of protection starts by examining everything on the library walls...  


Hint 2:  Access to the places of protection starts by understanding the functions of the map in the library.  


Hint 3: Turn on the marker switches on Myst Island to activate locations on the map in the library. Rotate the Tower to locations that turn the line red by clicking and holding the flashing icon on the map. Go to the Tower to find the access keys.