[9-14] E2M7: Underearth (Secret Level)

To the left of the gold door, push in a brick sticking out of the wall. This lowers a nearby column, granting you a Quad Damage.

After passing through the gold key door, you will enter a room with a winding bridge over a slime pit. Once across, look back over the slime pit. Underneath, you will see a small opening. Jump into the pit and enter this area to find the Bio-suit.

As you exit the Bio-suit alcove, you will see three pillars. Beyond the third pillar, dive below the slime to find the Red Armor. Use the button on the wall to exit the slime.