When trying gain access to the courtyard in the back of the Fenix Estate, you will encounter a door that can be kicked but won't open. If you use the Torque Bow to fire an arrow at the lower left-hand corner of the door, you will trigger the propane tank that is on the other side, but not set it off. Now, kick the door again and it will open. You can now use a grenade to seal off the Locust Emergence Hole as well as grab the ammo that is in the courtyard. Then, head back out and go up the stairs to the left of the door. Go around the hallway and to reach the two big open windows. Press Y to zoom in on the door and it will still be wide open, but the game will say that it is blocked. This also works with the frag grenade, but it is difficult to do because of the grenade bouncing off the walls.