Hi there,
People always ask if you have a key, but if you know exactly where the LEVER of the door is you can position your camera correctly move your mouse around where the lever should beand when you see the lever use it and should open! (works in SM and VC Doors all of em so if you dont want to destroy the last door with the cannon go to the left of the entrance and look for the lever, tried them worked fine)
hf