there's an elevator in one of the buildings. shoot the button with an arrow and it will come down.
also, there's a way behind the big crate boxes
from the top of roof/balcony area:
also you can break glass windows with sword, and break all non-metal doors with the sword if you don't have a key/cant pick it
just hold the attack button until Garrett grunts and pulls the sword back then hit the door, do this 3-4 times until it breaks open.
Of course this approach makes a lot of noise and can alert guards.