there a treasury on the main floor, and the text say i can get in from the floor above, but i can't find entrance where is it?
also do i get anything good for killing all creatures in zoo?
there is a room north west corner of the zoo, that i can't get into, anything in there?

Spoilers ahead:
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You can't get IN the treasury, but you can get stuff OUT: You will need the contents of the Constable's safe and an odd device in the King's apartment.

There are keys around for that door, and some others in the neighborhood, but these REALLY need to be used in JUST THE RIGHT SPOT: move your cursor over the door, watch for it to turn to a hand, then get the key from inventory and try it there.

Happily, there is more than one way into that area-- have you played with the prince's abandoned toys?

Oru