From the entrance, turn to your right and press the monitor on the wall. If you're having trouble finding the red key, it is located in the room where you get surrounded by Mancubi. You'll need the red key, but you should already have that. Repeat the same process -running across the pits, hitting the switch, jumping on the elevator, shooting the button- and the door for the Demon Artifact will now be open. It will soon bring you up and you'll need to shoot a switch to drop another platform.
Run back across both drops and right an immediate right onto an elevator. You'll need to make some running jumps to a switch that was hidden by a wall (it probably dropped the first time you were there). Go back to the room that was locked by the blue key and jump down the first drop. Once you have both the yellow and red keys in your possession, you'll be able to acquire it. The first Demon Artifact is found on the first secret level.
