[9-15] E2M4: The Ebon Fortress

You'll start by hopping down into some water. Head right and look for a cave entrance on the left, right next to a grenade launcher. Go inside, then into the next watery room. Take the entrance on the left, and immediately turn left after entering. You'll see a platform with steps ahead, and dragon windows high up on your right and left. Go straight until you hit a wall, then turn left. Follow the passageway until you reach an elevator. Ride it up, cross the bridge to the next room, head down the stairs, and then turn around to your left. There's an inlet next to the stairs – shoot the wall there. It'll open up to reveal rockets and a big health boost (200 life). Nice find!

Now, head back up the stairs and to the right, where you'll see a slanted wooden floor against the wall. Turn right again and look at the wall ahead. You're looking for a section of wood. Shoot it, and it'll open up. There's a small ledge to the left along the wall that will let you get to it.

In the room where you grab the silver key, get off the moving platform and turn right. Head into the gap that has toxic slime below. Swim down and to the left; you'll find a secret area containing the red armor. Grab it!

Let's find another secret from the very start. Hop into the water and hug the wall to the right of the island where the grenade launcher is. You'll sink into a secret area that has Quake Damage (likely an armor or power-up) and Yellow Armor.