Every door except the easternmost one in the hallway you start the map in leads to one of the three rec rooms. In each rec room, a part of the northern wall has a blue paneling. Open any of these to find a secret passage (sector 147) to the bridge. (On hard skills, there are two energy cell packs in this passage.)
At the very south of the eastern computer room, use the northern or southern side of the mainframe second from the east. It will act like an elevator and lower. Ride it up, and then jump across the other mainframes to the northwestern closet (sector 66) that contains a plasma gun (not on easy skills) and a supercharge (not on hard skills).
The back wall of secret #2 is textured differently; it is a door leading to a megasphere (sector 193). Note that opening it also opens the computer room's northern wall, releasing a group of (skill dependent) nine/four/none troopers and none/five/nine imps into the room as well. In their alcove are two stimpacks and a box of bullets.
Using the mainframe elevator for secret #2 will also affect the inner corner of the table in the green room to the south. If you get there fast enough, it will lift you up, allowing you pick up the backpack (sector 166) (and two medikits on easy skills).
In this same room, two of the gold panels in the south have green lights. These are both one door that opens to a stash of items (sector 170). Here, you will find two boxes of bullets, two boxes of shells(, three energy cell packs on medium and hard) and two (three on easy) medikits.
Routes and tricks
As with many other levels in Icarus that have "teleporter" or "begin simulation" exits, a death slide can be performed on this level in the exit hall. The rocket launcher on this level can be used to do so by blasting yourself off of the red computer panels with your back facing the teleporter, but the fastest way is to have monsters kill you. It's easier to do on Nightmare difficulty, where gunfire is constant, and you can run toward the exit as a bullet hits and kills you, sending your corpse under the exit. On Ultra-Violence or lower, however, the monsters are slower, so you will need to let the Cacodemon bite you to lower your health faster.