[9-6] E1M5: Gloom Keep

From your starting position, jump right off the bridge. Look for a column-like structure sticking out of the wall. Beneath the water, you'll find an opening leading to a ledge with a box of nails and 100 health.

Cross the starting bridge and turn right. Follow the walkway and pass through the gate. Proceed forward and right towards a stairway. Jump onto the bannister, then jump across to a jutting ledge. Run along this ledge to a platform containing an ogre, rockets, and armor.

Cross the starting bridge and go through the gate. Follow the passageway to a room with a Y-shaped platform. Take the right fork and continue until you enter a large room. Ahead and to the left is a staircase. To the right is a square area with a central column. Approach the column, jump, and hit the torch with your head. A door will open behind the column, revealing yellow armor and a touchplate to reopen the wall if it closes.

In the same large room as secret #3, climb the staircase. To your right, you'll find another set of stairs leading to an octagonal room with a slipgate (a portal that teleports you) to the gold key. Go behind this slipgate and step through. You will reappear near the start, on top of the building you first entered. A quad damage power-up is nearby.

After falling down the passage leading to the exit slipgate, turn around. The wall will appear 'turned' with roll added to it. Shoot this wall to open it, revealing a slipgate that leads back to the gold key doors.