Even though the gate in the Mama Dolce's Shipping Yard says it requires a key, the key is nonexistent. If you are really curious, to see what is beyond the gate use this method; using the metal barrels, stack them on top of each other to make a stair case (you will need 3). Stack 2 on top of each other next to the gate and wall (for stability). Then place another barrel next to wall and next to the stacked barrels. Carefully jusmp on the first barrel (it is very easy to knock them over causing you to stack them again). Jump on top of the next barrel and over the gate. Beyond it is a white void. Even thought you are not going to any other location, your map will say you are heading to other locations, such as Arlington Metro North.