[9-6] E1M5: Gloom Keep

Secret 1: Right after you spawn, hop off the bridge and look for a column-like structure sticking out of the wall. Under the water below it, there's an opening. Dive in to find a box of nails and 100 health. Grab it to keep your health topped up early on.

Secret 2: Head across the starting bridge and take a right. Follow the walkway until you pass through a gate. You'll see a stairway ahead and to the right. Instead of taking the stairs normally, jump onto the bannister and then leap across to a ledge jutting out from the wall. Follow this ledge to a platform where an ogre is waiting. Take him out and collect the rockets and armor waiting there.

Secret 3: Cross the starting bridge again and go through the gate. Follow the passage until you reach a room with a Y-shaped platform. Take the right fork and continue down the passage. You'll enter a large room. Look forward and to the left for a staircase, and to the right for a square area with a central column. Go up to the column and jump to hit the torch on top with your head. A hidden door will open in the wall behind the column, revealing yellow armor and a touchplate to open the wall if it closes on you.

Secret 4: From that same large room in Secret 3, climb the staircase. To your right, you'll find another set of stairs leading to an octagonal room containing a slipgate that takes you to the gold key. Don't go through it just yet! Go behind the slipgate, and you'll find a Quad Damage power-up. Grab it before heading through the slipgate. Once through, you'll appear near the start, on top of the building you first entered.

Secret 5: Eventually, you'll fall down a passage that leads to the exit slipgate. Before you jump in, turn around. You'll notice a wall that looks a bit 'off' – it has a rolled texture. Shoot this wall, and it will open up, revealing a slipgate that takes you back to the gold key doors. This is a handy shortcut if you need to backtrack.