Beware of this Quad: it sits on a trap door, that will drop you in acid, right in front of the slipgate out. Endure the pain and run around the corner, a second slipgate will transport you to some goodies.

Underneath these stairs is a switch. Press it, and take the slipgate out. Take the stairs down to the red brick room - a secret room is open now.

BTW, you have to shoot the red skylight to continue beyond this point.

I have heard about serial killers, but serial secrets...?

It start in this room. Shoot the wall under the Pentagram of protection. Secret room with goodies....

...Then shoot the wall under the Quad damage. A door slides aside, and give you access to a secret slipgate...

...and actually entering the slipgate is yet another secret! It sends you to...

...This ledge here. See the slit on the left? Stick a few grenades in there. It cures the Vore's breathing problem, and opens another secret room - goodies inside.

Jumping down from the platform, and entering the secret room counts as two seperate secrets...

...You can alternatively get to the platform secret by shooting this switch. Whatever makes you happy!

Stand on the extra-wide wide step, and you can ride it comfortably up, when you shoot. Else you will have to walk the long, agonizing way around. Oh, it's hell to be a Marine.

...Now, here is another secret...

...and, right across from it, yet another one. See what i mean with 'serial'?