E1, M6: Central Processing
This map contains 4 secrets, plus an extra hidden space with an automap.
Secret 1
In the red key door, there is a blue key overlooking a huge slime pit. Drop down into the slime and turn right to find a biohazard suit. Then, go back to the area across from where the blue key was. You will see a dark tunnel that leads to a soulsphere.
Secret 2
Inside the same slime pit, take a right after you emerge from the dark tunnel in secret 1. You will find a blue piece of armor and other goodies. This is secret 2 and the exit from the slime pit.
Secret 3
There are two ways to get to this one.
Near the blue key door is an outdoor area with lots of slime and some bars with a yellow key and imps behind them. If you walk to the blue key door, then turn around and come back into the outdoor area, a platform will lower with a biohazard suit. There is a secret door located behind the biohazard suit.
ALTERNATE ROUTE: Inside the blue key room, you will find a green piece of armor and the yellow key. You can open the wall behind the green armor to get leading to the same secret area with the biohazard suit.
I used the alternate route in the gameplay video below, although the first route is a shortcut to get the yellow key.
Extra Hidden Automap
In the blue key door maze area, there is a tunnel with some armor bonuses in the shape of an arrow pointing to a brown patch of wall. It is a secret door containing the automap.
Secret 4
The outside area where secret 3 is has a tunnel in the slime hidden behind a wall. This leads to a dead end until you walk over the steps to the yellow key. Walking over them triggers another tunnel to open with some items and a door at the end.
The door leads to an outdoor courtyard with a soulsphere.