E1M1: Cradle to Grave
Jump out of your tomb, moving forward and turning to your right. Open the doors to get outside. Walk down the earthen steps to your right and open the gates. Behind the tomb to your right is a cultist who holds the Skull key. Kill him and get the key. Now, enter the Morningside Cemetery. Keep moving forward until you get to viewing area.

Open up the curtains over to your right, and follow the passage to the right of the organ until you get to the crematorium door on the right side of the passage. Enter the crematorium, collect the Dagger key, then continue on down the passage to the Dagger key door. Open it, and jump through the hole in front (and to the right) of you. Push the symbol to end the level.
E1M2: Wrong Side of the Tracks
Go through the hole, and shoot the TNT barrels to your left, blowing a hole in the rail car. Shoot the TNT barrels in the car to blow the other side to the car. Jump up in the car, walking through it, until you come to another rail car. Over on the left side is a narrow space, which will allow you to walk by it. As you come out of that space, you'll see a button in front of you. Push it, and the rail car will rotate, revealing a door on the other side of the rail car. Jump through the middle of the car, and turn to your left to see the newly revealed door.

Open the door, walk down the stairs, and follow the stone path to the "Miskatonic Station." Enter the station, walk up the stairs, and you find yourself at a Ticket booth. Walk around it, and enter through the "No Admittance" door. Collect the Moon key, turn around, and walk til you're just under the "Miskatonic Station" sign, and turn around. You'll see two staircases to your left and right. Follow the left one up, open the Moon key door, and get the Fire key.

 Then retrace your steps, and go up the right one. Follow the passage until you get to the room with JoJo posters and the Fire key door. Open the gate, and follow the passage to the end, and wait for your train to come in. Hit the symbol on the front of the train to end the level.
E1M3: Phantom Express
Follow the ledge either way until you get to the Fire key door at the rear of the engine car. Walk over the coal car, and jump down in front of the door to the first passenger car. Open it, fight your way to the second passenger car (the Skull key door is in this car), fight your way through it, and you'll get to the storage car. Over on the left side is the door which leads to the dining car (strange that the storage car is between the passenger cars and the dining car).

Grab the Skull key in the dining car, and return to the 2nd passenger car. As you enter the 2nd passenger car, use your Skull key on the elevator to your left. Ride it up, open the door, grab the fire key, and ride it back down. Now head for the Fire key door all the way back at the beginning of the level. Open it up, and walk around the furnace to the very front of the car.

 Turn to your right to see the train controls. On the right side, you'll see a lever. Hit it, and turn back toward the furnace. You'll see two switches on both sides of the furnace's grill. Hit both of them, step back, and wait for all hell to break loose, ending the level.
E1M4: Dark Carnival
Walk forward until you get to the over-turned coal car, and turn to your right. You'll see a passage in the rock face. Enter it, and follow it along to the carnival entrance. Jump down and head down the path to your right, across the little wooden bridge, and into "Cougar and D'arc's Pandemonium Shadow Show."

Walk past the ticket taker, and straight along until you get to the ramp. Take note: the Moon key door and another ramp are over to you left. Go up the ramp, and turn to your right for some more fun and games. Walk by them all, JoJo the main attraction, so follow the directions on the sign and go to the left. Open the door to the JoJo attraction, you'll see two pillars and a high wire between them. Go to the pillar on the left and push the button to ride the lift up, walk across the high wire, collect the Dagger key, and walk back over the wire. When you get back across, push the button to call the lift back up, and ride it down. Turn to your left and go out the door under the "Exit" sign. You'll find yourself in another part of the carnival. Turn to your left, and walk all the way to the end, then turn right, and you'll see the Dagger key door over on your left.

Enter the Dagger key door, and you'll find the entrance to the ticket booth with the Moon key. Grab it, and walk back out to the carnival. Take a left at the Punch-O-Meter, and enter the Happy-Go-Pukey using the Eye key. Fight the gargoyle and pick up the Moon key. Go through the passage under the "Exit" sign, and you'll find yourself across from the Moon key door. Enter the Moon key door and you'll come to a bridge that will blow up just as you turn the corner.

Now you could be boring, and jump in the water, take the underwater passage over to your left to Level 5. Instead, use the pillars to jump across to the other side. Blow the crack in the wall from the last pillar, then jump over. Dive into the small pool of water, swim through the underwater passage, and surface into a small cave. Before you, you'll see a stone with three skulls on it. Push the skulls to the following combination: Dagger, Eye, Moon. And it's off to the secret level.
E1M8: House of Horror
Follow the passage to a gate. Open the gate, go up the ramp, and open the face to the fun house. Follow the path along until you get to the spot where you have green water to your left. Jump in and follow it along until you get to gate which blocks your way. Shoot out the bars with the zombies behind it, and jump up in it. A security booth will open before you. Jump into it, and pull the lever to open the gates.

 Follow it along until you see an "Under Construction" sign, quickly jump into the niche to your left, and take the lift down. You'll see another section with green water past the unconstructed part, so jump up in it, and continue along. Eventually, you come to a large room, with the Skull key beyond your reach. Drop down, and grab the Diving suit from behind the waterfall. Walk toward the "Spine Crusher" sign, and you'll drop down underwater. Go through the passage to your right, and continue along until you get to a metal room. Swim into the room to your left, turn around, and push the switch on the left side. A room will open up in front of you releasing some bone eels, and a passage will open over to the left. Swim out of the room, and take the passage to your left. Follow the passage, and you'll eventually surface in a torture chamber and the Skull key door. Take the stairs in front of you, and collect the Skull key from the ledge.

 Return, and open up the Skull key door. Take the path to your left, and follow the long, winding passage until you find a wooden door on your right. Open it, and follow it up to a room filled with wood. Jump out the window in front of you onto a sloped ledge, and shoot out the X-shaped boards to your right. Jump through the newly opened space into an area filled with TNT barrels. Shoot the barrels until you find the one which blows a hole in the wall (it's all the way around). Jump into the hole, and into the small pool of water. Follow the underwater passage and surface. Jump out of the water and hit the symbol to end the level.
E1M5: Hallowed Grounds
Walk across the open aired area into the next building. Over to your left, is the entrance into a big hallway with lots of pillars. Enter it, and turn to your right. Walk all the way down until you get to the wide wooden door on your left. Open it, and keep walking, past the Moon and Skull key doors, until you finally get to the Skull key. Don't go back to the Skull key door yet. Instead, take the door to your right into a large room.

Up on the right ledge, you'll see a doorway, follow it along to a small pool of water on your right. Jump in, swim to the end, and push the switch. Swim back, and a staircase will be opened to your right. Climb up stairs, listen to the message, and open the curtains on the left fork. Jump down, and walk through the doors to your left. This will take you to the Skull key door. Open it, and follow the stairs up until you come to a room with several doorways. Take the one to your immediate left, and drop down the hole in the floor. At the end of the passage, you'll see a differently colored wall, push it, and enter into the next room (you could take the long way around through the courtyard, but this is the quickest way).

Keep walking forward and take the Moon key over the left side of the room. When you pick up the key, the gate in front of you will open up taking you back to the big hallway from the beginning of the level. Follow it back around to the Moon key door. Open the door, and follow the stairs down. At the bottom of the stairs, take note of the Spider key doors in the room on your right, but take the passage over to your left, until you come to a lift. Take the lift up to the wine storage area, and pick up the Spider key. Return via the lift to the Spider key doors, and open the left one. Follow the passage, turn to your left, cross the bridge, and push the symbol to end the level.
E1M6: The Great Temple
Follow the passage along until you get to a pool of water with a bridge over it. Jump into the water. Dive down and turn around. Go through the underwater passage into a larger room. To your left, you'll find another underwater passage, which will take you to some stairs. Climb the stairs, and follow the passage until you find the wooden bridge on the right side of the passage. Cross it, and push the switch on the left side of the niche, and turn back toward the bridge.

 The bridge will lower slightly (making it accessible to your starting position), and some double doors flanked by gargoyles will open up to your right. Enter the doors, and go to your left. Climb the stairs and follow the passage to the room with the stained glass (both paths into the room lead to the same place). Go up the stairs into a large shooting gallery (you're the target). Work you way to the other side of the room, and go through the gray doors. You'll find yourself in a room with with the Skull key door. Walk to the door, and turn to the left.

 Follow the path along, and drop down into the area to your right. Open the wooden doors, walk-in, kill everybody, grab your reflective shots, and go back out. When you jump back up, the area in front of you will open up. Enter into the room with the switch. The door behind you will close and zombies will be released. Kill them all, and the next room. Again, the door will close behind you, but grab the Skull key and another door opens, returning you to the room with the Skull key door. Enter the Skull key door, and follow the passage down to a room with three short staircases. Climb up both of the ones to your right, and pull the levers. When both are switched on, the Fire key will rise up in the space across from the third staircase. Grab it, and hit the Fire key switch. Enter into the door which opens, and make your way across the fireballs. At the end of the passage will be a trolley of some sort with a switch. Push the switch, and duck down to avoid the flame-throwers. When you get to the end of the line, quickly get out to avoid being blown up.

 Climb the stairs, and walk along until you get to another Fire key switch, push it and a niche opens up next to it with another switch inside. Push it, and the wooden doors on the other side of the room will rise up. Go through it, and you'll find yourself in a room with a ramp around it. Go up the ramp, and collect the Spider key. After grabbing the Spider key, a door will open up behind you. Follow the passage (ducking under the flame-throwers), and you find a switch at the end of the hall. Push it, and you'll now be on the upper ledge of the shooting gallery. Follow the path along, go up the stairs, and you'll see the Spider key door on your left. Open it, go up the stairs, and pick up the Moon key in the middle niche on your right. After killing all the zombies, go out through the other door, and you find yourself facing the Moon key door.

 Open it, and walk into the teleporter. You'll find yourself in a room with Guns Akimbo up on a pillar. Push the pillar, and the wall around the room will rotate revealing a room with zombies, kill them. You'll see a switch on the left side of the room, push it, and get back in the central area before the wall rotates. You'll need to repeat this procedure with the next room. After the third rotation, the symbol to end the level will be revealed.
E1M7: Altar of Stone
Go up the stairs in either direction. When you get to the wooden bridge leading to the altar in the center, cross it. This will get the attention of Cheogh, and the final battle of episode one will begin. Kill him to end the level.