Doom/E4M3: Sever The Wicked

E4M3 takes place in a mix of an open area, and inside a building.

Starting region
When you start, there is a shotgun directly ahead. If you are having trouble, there are a few items to collect as well. You can proceed forward with a left turn to flip a switch, which raises a bridge that leads to invulnerability. Directly behind the starting point is a small drop containing a berserk, invisibility, and a backpack. If you head south and to the right, you can find a chaingun. Finally, directly ahead of the starting point and along the southern edge of the chasm is another invisibility.

Red key
You can collect the blue or red key when you start, but it is easier to get the red key first. The first step is to head down the stairs visible from the starting point.

There are two routes. The fastest route requires going up the stairs, and through the corridor. When you reach the door, some imps will attack you from behind. On the other side of the door is the platform containing the red key, but you can optionally take the left exit to retrieve a plasma gun. To get the key, jump down into the pit, and flip the switch near the pit. This lowers the red key which you can collect.

The other route requires taking the down staircase, a longer route but also an alternate exit. This will lead to a room containing a lift, which lowers and reveals a teleporter and two flanking alcoves containing monsters. While you can collect ammo in this room, the teleporter is on the other side. This brings you to the southern section of the map, where you get attacked by approaching monsters. From the teleport, you need to head north to the switch to lower the red key.

Once you have the red key, you need to return to the starting area. The southern teleport brings you to the north-west room, but a faster exit is in the western alcove. Use the left wall (marked with a different texture), which leads to a teleport heading to the starting area.

Blue key
When you have the red key, head north of the starting area for a direct route. If you don't have it, you need to jump down into the left half of the chasm, and press one of the two visible switches to lift yourself to the platform and circle around to the back.

The blue key is north of the central pillar.

Exit
With both keys, jump into the eastern half of the chasm. The red key door is at the end, which leads to a specter and a staircase. Once you go through the blue key door, the exit should be accessible.

Secrets
In this map, you can only get a 90% rating on secrets visited, because some triggers for awarding a secret are obstructed. However, the secrets are located as follows:
 * When you head up the stairs towards the red key, a corner wall has a different texture. It opens when used, or if you approach the next door.  It contains blue armor, some health, ammo, a backpack, and a chainsaw. It also released up to four imps from behind.
 * In the room left of the switch to lower the red key, there is an opening. The secrets are the the north-east and south-east corners of the room, and count twice.  However, they are obstructed by torches.
 * From the above secret, open the north wall. This leads to blue armor, a soul sphere and ammunition. This accounts for 19 secrets, and you must step on each step to claim all secrets.