Library

The museum or library levels, along with the observatory that has the same style, are truly fascinating. Many of the game most obscure collectibles can be found here.

The outside of the building will kinda make you think it is a museum...

But as soon as you enter, the room has a huge resemblance to Myst, the game from 1993.

And as a homage to the original game, you will have a secret passageway. I won't spoil it on where, use the Walkthrough for that.

 

As a wise reddit user once asked,

Once a species acquires the gift of knowledge, what do they do with it? Catalog it!

And so did the Zu catalog everything they learned since the apparition of the monolith. You can notice they were aware of the visitors, since some buildings reference them.