If you have the proper card, you can take the forest part to the south from the tank you have to fight. The proper way through the maze is:
Left, Left, Up, Left.
If you have... card three I think it is, you can reenter the building... otherwise you'll have to wait until you get to one of the last portions in the game and go south in the building to reach it (the place where you fight Firetrooper is attached to the place where you need the flashlight to see, which also has Dr. Pettrovich's daughter, and connects to the same building with Shotgunner... sounds right in my memory anyway.
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