Doom/E3M1: Hell Keep

You begin the level staring at a pillow with an eye in the center. Press it to raise the pit you are in to ground level. There will be three Imps who will notice you. Ignore them and run toward the building, striking the switch to the left of the door. There are also two boxes of bullets you can acquire. The door will open to expose two Cacodemons ("Cacos"). You want the Cacos to see you, but run away from the building toward the back to avoid being shot at by either the Cacos or the Imps. This will draw the Cacos out of the building, and allow them and the Imps to get between each other. This will keep them busy fighting each other so that you can run into the building, possibly without being hit.

You will find a 25% health pak along the forward path, if you took any shots from the Imps or the Cacos.

You have two choices at this point, you can run forward along the runway over the lava pit, which gives you access to a shotgun, or you can go to your right and continue on to the rest of the level. Note that if you don't take the runway, you will have to complete the level with only a pistol; the runway is the only way to get a shotgun.

Getting the shotgun
If you continue forward, you must keep moving fast, because as soon as you step on the runway it begins to sink into the lava; if you do not reach the end and the invisible room before the runway collapses, you will have to go around and may die from burns before you can reach the escape from the pit. In fact, since this is the start of Episode 3, if you miss and fall off the runway, you'll take so much damage from the pit that you're probably better off allowing yourself to die and starting the level over.

As you run along the runway you will pick up the shotgun. At the end of the runway is a hidden exit, where the invisible room has three Imps and a case of shotgun shells that you'll end up automatically taking. You'll need to kill the Imps (using the shotgun), then exit to the side, and press the switch to open the door out. At this point you will be at the same place as if you had not taken the forward option. Turn to your left to continue, but be careful that neither any surviving Imps or Cacos are in this area; if they are you, may have to kill them or may do so if you want to maintain a 100% kill rate.

The rest of the level
Either taking or rejecting the lava pit now brings you to the side option at the front entrance of the building. There is a 25% health pak along this route as well. Next you will come upon a door that opens to a courtyard where there are four Imps and two Cacos, as well as a 25% health pak. Run for the next door on the right, and if you want to attack them, do so later. The reason for this is if you are fast enough, the Imps might be too busy and not follow you through the door, and the Cacos can't (they're too big). (They might also fight each other and kill or weaken some in the process.)

Entering this door leads to a tight corridor and four Demons. You will need to kill them to get through the corridor. Once you kill them, then you can go back and take on the Cacos and Imps that were in the courtyard if you want. You'll have a better environment for fighting since only the Imps can come after you; the Cacos can't get through the door, and you can step to the side out of the range of their fire attacks.

At the far end of the corridor is a door. This is a one-way door; once it closes you can't go back, so if you want 100% kill you have to go back and make sure everyone behind you is dead before going through this door.

You will be in a room with some pillars, a skull, some health, armor and shotgun shells; grab anything you can. There will be another door in front of you where eight imps will be present; be ready to shoot anything in the doorway as soon as you see them.

Kill them all to proceed to a gray room with a standard exit door. Go through the door into a courtyard where more ammo and health are present. Load up on what you can, then step on the white pentagram square in the middle of this room to end the level.