1. When exiting the nailgun room via an arch, shoot the brick on the ceiling to activate the lift nearby. It leads to a Yellow Armor.
2. In the portal hall there is a Mega Health behind the crates to the left.
3. In the watery pit where you drop down to hit the wall with the blue mark to open the room with a Mega Health.
4. In the room with the gold key you need to shoot 3 switches in sequence:
 - behind one of the crates
 - above the crates with the gold key
 - near two pipes downstairs
 and then quickly catch the rising platform to jump from it to the gold key. Behind the gold door there is a Red Armor.
5. Gold door from secret #4 allows you to access the upper ledge of the SSG room. Go to another hallway to a dead end with a lamp on the ceiling. Shoot the lamp to reveal a Quad.