[9-30] E4M8: The Nameless City (Secret Level)

From the start, follow the passage beneath the gold key platform. Take the right passage up a ramp. Press the wall button to the right to open a passage with zombies. Past the zombies is a platform leading to a small room with a shambler. Jump into the hole in the room to land on a ledge with the red armor.

In the room from step #1, there's a large hole overlooking another hole with a small ledge. Jump to this ledge. Look down to find a small ledge halfway down with health and a Quad Damage. Jump to this ledge to collect them.

After collecting the Quad Damage, jump into the water below. Press the button on the right side of the room to lower a walkway. Ride it up. Jump into the square cage in the middle and activate the button inside. The cage will lower into a zombie-filled room. Shoot the wall switch to exit the cage. Follow the passage out of the dark room and press the switch at the end to activate an elevator. Ride the platform up and jump through the window. Follow the passageway to the gold key. After collecting it, go to the gold doors at the end of the long hall and enter.

After entering the silver door, turn right and go up the ramp. Kill the zombies below the mesh. Drop through one of the triangle-shaped openings to get under the mesh and press the button to exit.