Down the first lift, there is a hidden switch (linedef #5840) in the small place far on the right that opens a room for the berserk
Just before grabbing the yellow key, just look on your right to open a small place for ammo boxes.
The small L with many armor bonuses after the yellow bars has a hidden switch (linedef #5929) that reveals a green armor.
Before falling in the moat (second screenshot), jump on the right: the nukage up there is secret.
When you grab the rocket launcher, a heavy weapon dude comes from your left. Behind him, another hidden switch (lindedef #1941) opens a room with rad shielding suits, you will need them.
Don't come back in the yellow key room, fall down and follow the brown and damaging nukage to a supercharge.