Doom/E1M2: Nuclear Plant

As soon as you start, sprint forwards and kill the two marines in the corridor. Sprint all the way to the end where there is a security vest for you, if you need it. Now, work your way around the room, killing the Imps and marines as you go. Once it's all clear, head up the lift in the centre section of this room to get a shotgun, and check the lift in one of the corners for a medikit and a box of bullets. Now, head around to the side of the centre section facing the side of the room with the two non-keycard doors. You may notice a discoloured wall section next to the light. Open it, and you'll find a secret area. Pick up the security vest in here if you need it, but most importantly, pick up the Backpack! You've now got double ammo capacity. Throw the switch in here, then go back out and through either of the doors.

Go up the stairs, killing as you go, and at the top clear out the room of marines and the Imp, and you can pick up the goodies as well as the red keycard. Facing outside, go back down the left-hand staircase and go through the open wall to outside. Kill the massive amount of shotgun marines out here and pick up all their ammo, and grab the Soulsphere. Keep going around, though; at the end you'll find two boxes of bullets and the Chaingun!

Go back to the room you started in, and now you can go through the red keycard door on the left-hand side. Kill the marines and go to the right. In the slime room, kill the Imp, then sprint across the slime to the middle platform. Here, throw the switch. This opens a dark maze section full of enemies. You may wonder why I told you to do this, but the maze is full of ammo and health, plus another security vest and two secret areas. At the far corner of the maze is a wall section between two grey columns - open it to reveal a small room with another Backpack in it. On the right-hand side of the maze (as you're looking into it) is a fading-light room with the security vest in it. However, you can shoot the wall behind it with a gun to open another secret area. Follow the stairs up and kill the marines at the top. Shoot the barrel in the corner to kill the Imp in the side room, and throw the switch to make the central pillar lower and allow you to grab the Chainsaw!

Head back out to the red keycard door, then go straight ahead and up the stairs. The lift to the left goes down to the side room you killed the Imp in, which has a medikit and a box of shotgun shells in it. Go back up and navigate the slime path room, and at the end check the discoloured wall on the left for another secret door which leads down to a ledge above the next room, which is full of Imps, marines and barrels. Clear it out, then go back up and use the lift to grab another box of shotgun shells. At the end of the room, flip the switch to open two doors on either side, and go through either and follow the path around to a staircase leading down to the exit door.

A bit of a sneaky tactic; the exit room is full of marines. Kill them, but watch out for the two Imps in the low section next to the exit switch. Throw the switch to leave the level.